import { ObjectLiteral } from '../../common/ObjectLiteral';
import { TypeORMError } from '../../error';
import { QueryFailedError } from '../../error/QueryFailedError';
import { QueryRunnerAlreadyReleasedError } from '../../error/QueryRunnerAlreadyReleasedError';
import { TransactionNotStartedError } from '../../error/TransactionNotStartedError';
import { ReadStream } from '../../platform/PlatformTools';
import { BaseQueryRunner } from '../../query-runner/BaseQueryRunner';
import { QueryResult } from '../../query-runner/QueryResult';
import { QueryRunner } from '../../query-runner/QueryRunner';
import { TableIndexOptions } from '../../schema-builder/options/TableIndexOptions';
import { Table } from '../../schema-builder/table/Table';
import { TableCheck } from '../../schema-builder/table/TableCheck';
import { TableColumn } from '../../schema-builder/table/TableColumn';
import { TableExclusion } from '../../schema-builder/table/TableExclusion';
import { TableForeignKey } from '../../schema-builder/table/TableForeignKey';
import { TableIndex } from '../../schema-builder/table/TableIndex';
import { TableUnique } from '../../schema-builder/table/TableUnique';
import { View } from '../../schema-builder/view/View';
import { Broadcaster } from '../../subscriber/Broadcaster';
import { InstanceChecker } from '../../util/InstanceChecker';
import { OrmUtils } from '../../util/OrmUtils';
import { VersionUtils } from '../../util/VersionUtils';
import { Query } from '../Query';
import { ColumnType } from '../types/ColumnTypes';
import { IsolationLevel } from '../types/IsolationLevel';
import { MetadataTableType } from '../types/MetadataTableType';
import { ReplicationMode } from '../types/ReplicationMode';
import { PostgresDriver } from './PostgresDriver';
import { BroadcasterResult } from '../../subscriber/BroadcasterResult';

/**
 * Runs queries on a single postgres database connection.
 */
export class PostgresQueryRunner extends BaseQueryRunner implements QueryRunner {
	// -------------------------------------------------------------------------
	// Public Implemented Properties
	// -------------------------------------------------------------------------

	/**
	 * Database driver used by connection.
	 */
	driver: PostgresDriver;

	// -------------------------------------------------------------------------
	// Protected Properties
	// -------------------------------------------------------------------------

	/**
	 * Promise used to obtain a database connection for a first time.
	 */
	protected databaseConnectionPromise: Promise<any>;

	/**
	 * Special callback provided by a driver used to release a created connection.
	 */
	protected releaseCallback?: (err: any) => void;

	// -------------------------------------------------------------------------
	// Constructor
	// -------------------------------------------------------------------------

	constructor(driver: PostgresDriver, mode: ReplicationMode) {
		super();
		this.driver = driver;
		this.connection = driver.connection;
		this.mode = mode;
		this.broadcaster = new Broadcaster(this);
	}

	// -------------------------------------------------------------------------
	// Public Methods
	// -------------------------------------------------------------------------

	/**
	 * Creates/uses database connection from the connection pool to perform further operations.
	 * Returns obtained database connection.
	 */
	connect(): Promise<any> {
		if (this.databaseConnection) return Promise.resolve(this.databaseConnection);

		if (this.databaseConnectionPromise) return this.databaseConnectionPromise;

		if (this.mode === 'slave' && this.driver.isReplicated) {
			this.databaseConnectionPromise = this.driver
				.obtainSlaveConnection()
				.then(([connection, release]: any[]) => {
					this.driver.connectedQueryRunners.push(this);
					this.databaseConnection = connection;

					const onErrorCallback = (err: Error) => this.releasePostgresConnection(err);
					this.releaseCallback = (err?: Error) => {
						this.databaseConnection.removeListener('error', onErrorCallback);
						release(err);
					};
					this.databaseConnection.on('error', onErrorCallback);

					return this.databaseConnection;
				});
		} else {
			// master
			this.databaseConnectionPromise = this.driver
				.obtainMasterConnection()
				.then(([connection, release]: any[]) => {
					this.driver.connectedQueryRunners.push(this);
					this.databaseConnection = connection;

					const onErrorCallback = (err: Error) => this.releasePostgresConnection(err);
					this.releaseCallback = (err?: Error) => {
						this.databaseConnection.removeListener('error', onErrorCallback);
						release(err);
					};
					this.databaseConnection.on('error', onErrorCallback);

					return this.databaseConnection;
				});
		}

		return this.databaseConnectionPromise;
	}

	/**
	 * Release a connection back to the pool, optionally specifying an Error to release with.
	 * Per pg-pool documentation this will prevent the pool from re-using the broken connection.
	 */
	private async releasePostgresConnection(err?: Error) {
		if (this.isReleased) {
			return;
		}

		this.isReleased = true;
		if (this.releaseCallback) {
			this.releaseCallback(err);
			this.releaseCallback = undefined;
		}

		const index = this.driver.connectedQueryRunners.indexOf(this);

		if (index !== -1) {
			this.driver.connectedQueryRunners.splice(index, 1);
		}
	}

	/**
	 * Releases used database connection.
	 * You cannot use query runner methods once its released.
	 */
	release(): Promise<void> {
		return this.releasePostgresConnection();
	}

	/**
	 * Starts transaction.
	 */
	async startTransaction(isolationLevel?: IsolationLevel): Promise<void> {
		this.isTransactionActive = true;
		try {
			await this.broadcaster.broadcast('BeforeTransactionStart');
		} catch (err) {
			this.isTransactionActive = false;
			throw err;
		}

		if (this.transactionDepth === 0) {
			this.transactionDepth += 1;
			await this.query('START TRANSACTION');
			if (isolationLevel) {
				await this.query('SET TRANSACTION ISOLATION LEVEL ' + isolationLevel);
			}
		} else {
			this.transactionDepth += 1;
			await this.query(`SAVEPOINT typeorm_${this.transactionDepth - 1}`);
		}

		await this.broadcaster.broadcast('AfterTransactionStart');
	}

	/**
	 * Commits transaction.
	 * Error will be thrown if transaction was not started.
	 */
	async commitTransaction(): Promise<void> {
		if (!this.isTransactionActive) throw new TransactionNotStartedError();

		await this.broadcaster.broadcast('BeforeTransactionCommit');

		if (this.transactionDepth > 1) {
			this.transactionDepth -= 1;
			await this.query(`RELEASE SAVEPOINT typeorm_${this.transactionDepth}`);
		} else {
			this.transactionDepth -= 1;
			await this.query('COMMIT');
			this.isTransactionActive = false;
		}

		await this.broadcaster.broadcast('AfterTransactionCommit');
	}

	/**
	 * Rollbacks transaction.
	 * Error will be thrown if transaction was not started.
	 */
	async rollbackTransaction(): Promise<void> {
		if (!this.isTransactionActive) throw new TransactionNotStartedError();

		await this.broadcaster.broadcast('BeforeTransactionRollback');

		if (this.transactionDepth > 1) {
			this.transactionDepth -= 1;
			await this.query(`ROLLBACK TO SAVEPOINT typeorm_${this.transactionDepth}`);
		} else {
			this.transactionDepth -= 1;
			await this.query('ROLLBACK');
			this.isTransactionActive = false;
		}

		await this.broadcaster.broadcast('AfterTransactionRollback');
	}

	/**
	 * Executes a given SQL query.
	 */
	async query(
		query: string,
		parameters?: any[],
		useStructuredResult: boolean = false,
	): Promise<any> {
		if (this.isReleased) throw new QueryRunnerAlreadyReleasedError();

		const databaseConnection = await this.connect();
		const broadcasterResult = new BroadcasterResult();

		this.driver.connection.logger.logQuery(query, parameters, this);
		this.broadcaster.broadcastBeforeQueryEvent(broadcasterResult, query, parameters);

		try {
			const queryStartTime = +new Date();
			const raw = await databaseConnection.query(query, parameters);
			// log slow queries if maxQueryExecution time is set
			const maxQueryExecutionTime = this.driver.options.maxQueryExecutionTime;
			const queryEndTime = +new Date();
			const queryExecutionTime = queryEndTime - queryStartTime;

			this.broadcaster.broadcastAfterQueryEvent(
				broadcasterResult,
				query,
				parameters,
				true,
				queryExecutionTime,
				raw,
				undefined,
			);

			if (maxQueryExecutionTime && queryExecutionTime > maxQueryExecutionTime)
				this.driver.connection.logger.logQuerySlow(queryExecutionTime, query, parameters, this);

			const result = new QueryResult();
			if (raw) {
				if (raw.hasOwnProperty('rows')) {
					result.records = raw.rows;
				}

				if (raw.hasOwnProperty('rowCount')) {
					result.affected = raw.rowCount;
				}

				switch (raw.command) {
					case 'DELETE':
					case 'UPDATE':
						// for UPDATE and DELETE query additionally return number of affected rows
						result.raw = [raw.rows, raw.rowCount];
						break;
					default:
						result.raw = raw.rows;
				}

				if (!useStructuredResult) {
					return result.raw;
				}
			}

			return result;
		} catch (err) {
			this.driver.connection.logger.logQueryError(err, query, parameters, this);
			this.broadcaster.broadcastAfterQueryEvent(
				broadcasterResult,
				query,
				parameters,
				false,
				undefined,
				undefined,
				err,
			);

			throw new QueryFailedError(query, parameters, err);
		} finally {
			await broadcasterResult.wait();
		}
	}

	/**
	 * Returns raw data stream.
	 */
	async stream(
		query: string,
		parameters?: any[],
		onEnd?: Function,
		onError?: Function,
	): Promise<ReadStream> {
		const QueryStream = this.driver.loadStreamDependency();
		if (this.isReleased) throw new QueryRunnerAlreadyReleasedError();

		const databaseConnection = await this.connect();
		this.driver.connection.logger.logQuery(query, parameters, this);
		const stream = databaseConnection.query(new QueryStream(query, parameters));
		if (onEnd) stream.on('end', onEnd);
		if (onError) stream.on('error', onError);

		return stream;
	}

	/**
	 * Returns all available database names including system databases.
	 */
	async getDatabases(): Promise<string[]> {
		return Promise.resolve([]);
	}

	/**
	 * Returns all available schema names including system schemas.
	 * If database parameter specified, returns schemas of that database.
	 */
	async getSchemas(database?: string): Promise<string[]> {
		return Promise.resolve([]);
	}

	/**
	 * Checks if database with the given name exist.
	 */
	async hasDatabase(database: string): Promise<boolean> {
		const result = await this.query(`SELECT * FROM pg_database WHERE datname=$1;`, [database]);
		return result.length ? true : false;
	}

	/**
	 * Loads currently using database
	 */
	async getCurrentDatabase(): Promise<string> {
		const query = await this.query(`SELECT * FROM current_database()`);
		return query[0]['current_database'];
	}

	/**
	 * Checks if schema with the given name exist.
	 */
	async hasSchema(schema: string): Promise<boolean> {
		const result = await this.query(
			`SELECT * FROM "information_schema"."schemata" WHERE "schema_name" = $1`,
			[schema],
		);
		return result.length ? true : false;
	}

	/**
	 * Loads currently using database schema
	 */
	async getCurrentSchema(): Promise<string> {
		const query = await this.query(`SELECT * FROM current_schema()`);
		return query[0]['current_schema'];
	}

	/**
	 * Checks if table with the given name exist in the database.
	 */
	async hasTable(tableOrName: Table | string): Promise<boolean> {
		const parsedTableName = this.driver.parseTableName(tableOrName);

		if (!parsedTableName.schema) {
			parsedTableName.schema = await this.getCurrentSchema();
		}

		const sql = `SELECT * FROM "information_schema"."tables" WHERE "table_schema" = $1 AND "table_name" = $2`;
		const result = await this.query(sql, [parsedTableName.schema, parsedTableName.tableName]);
		return result.length ? true : false;
	}

	/**
	 * Checks if column with the given name exist in the given table.
	 */
	async hasColumn(tableOrName: Table | string, columnName: string): Promise<boolean> {
		const parsedTableName = this.driver.parseTableName(tableOrName);

		if (!parsedTableName.schema) {
			parsedTableName.schema = await this.getCurrentSchema();
		}

		const sql = `SELECT * FROM "information_schema"."columns" WHERE "table_schema" = $1 AND "table_name" = $2 AND "column_name" = $3`;
		const result = await this.query(sql, [
			parsedTableName.schema,
			parsedTableName.tableName,
			columnName,
		]);
		return result.length ? true : false;
	}

	/**
	 * Creates a new database.
	 * Note: Postgres does not support database creation inside a transaction block.
	 */
	async createDatabase(database: string, ifNotExist?: boolean): Promise<void> {
		if (ifNotExist) {
			const databaseAlreadyExists = await this.hasDatabase(database);

			if (databaseAlreadyExists) return Promise.resolve();
		}

		const up = `CREATE DATABASE "${database}"`;
		const down = `DROP DATABASE "${database}"`;
		await this.executeQueries(new Query(up), new Query(down));
	}

	/**
	 * Drops database.
	 * Note: Postgres does not support database dropping inside a transaction block.
	 */
	async dropDatabase(database: string, ifExist?: boolean): Promise<void> {
		const up = ifExist ? `DROP DATABASE IF EXISTS "${database}"` : `DROP DATABASE "${database}"`;
		const down = `CREATE DATABASE "${database}"`;
		await this.executeQueries(new Query(up), new Query(down));
	}

	/**
	 * Creates a new table schema.
	 */
	async createSchema(schemaPath: string, ifNotExist?: boolean): Promise<void> {
		const schema = schemaPath.indexOf('.') === -1 ? schemaPath : schemaPath.split('.')[1];

		const up = ifNotExist ? `CREATE SCHEMA IF NOT EXISTS "${schema}"` : `CREATE SCHEMA "${schema}"`;
		const down = `DROP SCHEMA "${schema}" CASCADE`;
		await this.executeQueries(new Query(up), new Query(down));
	}

	/**
	 * Drops table schema.
	 */
	async dropSchema(schemaPath: string, ifExist?: boolean, isCascade?: boolean): Promise<void> {
		const schema = schemaPath.indexOf('.') === -1 ? schemaPath : schemaPath.split('.')[1];

		const up = ifExist
			? `DROP SCHEMA IF EXISTS "${schema}" ${isCascade ? 'CASCADE' : ''}`
			: `DROP SCHEMA "${schema}" ${isCascade ? 'CASCADE' : ''}`;
		const down = `CREATE SCHEMA "${schema}"`;
		await this.executeQueries(new Query(up), new Query(down));
	}

	/**
	 * Creates a new table.
	 */
	async createTable(
		table: Table,
		ifNotExist: boolean = false,
		createForeignKeys: boolean = true,
		createIndices: boolean = true,
	): Promise<void> {
		if (ifNotExist) {
			const isTableExist = await this.hasTable(table);
			if (isTableExist) return Promise.resolve();
		}
		const upQueries: Query[] = [];
		const downQueries: Query[] = [];

		// if table have column with ENUM type, we must create this type in postgres.
		const enumColumns = table.columns.filter(
			(column) => column.type === 'enum' || column.type === 'simple-enum',
		);
		const createdEnumTypes: string[] = [];
		for (const column of enumColumns) {
			// TODO: Should also check if values of existing type matches expected ones
			const hasEnum = await this.hasEnumType(table, column);
			const enumName = this.buildEnumName(table, column);

			// if enum with the same "enumName" is defined more then once, me must prevent double creation
			if (!hasEnum && createdEnumTypes.indexOf(enumName) === -1) {
				createdEnumTypes.push(enumName);
				upQueries.push(this.createEnumTypeSql(table, column, enumName));
				downQueries.push(this.dropEnumTypeSql(table, column, enumName));
			}
		}

		// if table have column with generated type, we must add the expression to the metadata table
		const generatedColumns = table.columns.filter(
			(column) => column.generatedType === 'STORED' && column.asExpression,
		);
		for (const column of generatedColumns) {
			const tableNameWithSchema = (await this.getTableNameWithSchema(table.name)).split('.');
			const tableName = tableNameWithSchema[1];
			const schema = tableNameWithSchema[0];

			const insertQuery = this.insertTypeormMetadataSql({
				database: this.driver.database,
				schema,
				table: tableName,
				type: MetadataTableType.GENERATED_COLUMN,
				name: column.name,
				value: column.asExpression,
			});

			const deleteQuery = this.deleteTypeormMetadataSql({
				database: this.driver.database,
				schema,
				table: tableName,
				type: MetadataTableType.GENERATED_COLUMN,
				name: column.name,
			});

			upQueries.push(insertQuery);
			downQueries.push(deleteQuery);
		}

		upQueries.push(this.createTableSql(table, createForeignKeys));
		downQueries.push(this.dropTableSql(table));

		// if createForeignKeys is true, we must drop created foreign keys in down query.
		// createTable does not need separate method to create foreign keys, because it create fk's in the same query with table creation.
		if (createForeignKeys)
			table.foreignKeys.forEach((foreignKey) =>
				downQueries.push(this.dropForeignKeySql(table, foreignKey)),
			);

		if (createIndices) {
			table.indices.forEach((index) => {
				// new index may be passed without name. In this case we generate index name manually.
				if (!index.name)
					index.name = this.connection.namingStrategy.indexName(
						table,
						index.columnNames,
						index.where,
					);
				upQueries.push(this.createIndexSql(table, index));
				downQueries.push(this.dropIndexSql(table, index));
			});
		}

		if (table.comment) {
			upQueries.push(
				new Query('COMMENT ON TABLE ' + this.escapePath(table) + " IS '" + table.comment + "'"),
			);
			downQueries.push(new Query('COMMENT ON TABLE ' + this.escapePath(table) + ' IS NULL'));
		}

		await this.executeQueries(upQueries, downQueries);
	}

	/**
	 * Drops the table.
	 */
	async dropTable(
		target: Table | string,
		ifExist?: boolean,
		dropForeignKeys: boolean = true,
		dropIndices: boolean = true,
	): Promise<void> {
		// It needs because if table does not exist and dropForeignKeys or dropIndices is true, we don't need
		// to perform drop queries for foreign keys and indices.
		if (ifExist) {
			const isTableExist = await this.hasTable(target);
			if (!isTableExist) return Promise.resolve();
		}

		// if dropTable called with dropForeignKeys = true, we must create foreign keys in down query.
		const createForeignKeys: boolean = dropForeignKeys;
		const tablePath = this.getTablePath(target);
		const table = await this.getCachedTable(tablePath);
		const upQueries: Query[] = [];
		const downQueries: Query[] = [];

		if (dropIndices) {
			table.indices.forEach((index) => {
				upQueries.push(this.dropIndexSql(table, index));
				downQueries.push(this.createIndexSql(table, index));
			});
		}

		if (dropForeignKeys)
			table.foreignKeys.forEach((foreignKey) =>
				upQueries.push(this.dropForeignKeySql(table, foreignKey)),
			);

		upQueries.push(this.dropTableSql(table));
		downQueries.push(this.createTableSql(table, createForeignKeys));

		// if table had columns with generated type, we must remove the expression from the metadata table
		const generatedColumns = table.columns.filter(
			(column) => column.generatedType && column.asExpression,
		);
		for (const column of generatedColumns) {
			const tableNameWithSchema = (await this.getTableNameWithSchema(table.name)).split('.');
			const tableName = tableNameWithSchema[1];
			const schema = tableNameWithSchema[0];

			const deleteQuery = this.deleteTypeormMetadataSql({
				database: this.driver.database,
				schema,
				table: tableName,
				type: MetadataTableType.GENERATED_COLUMN,
				name: column.name,
			});

			const insertQuery = this.insertTypeormMetadataSql({
				database: this.driver.database,
				schema,
				table: tableName,
				type: MetadataTableType.GENERATED_COLUMN,
				name: column.name,
				value: column.asExpression,
			});

			upQueries.push(deleteQuery);
			downQueries.push(insertQuery);
		}

		await this.executeQueries(upQueries, downQueries);
	}

	/**
	 * Creates a new view.
	 */
	async createView(view: View, syncWithMetadata: boolean = false): Promise<void> {
		const upQueries: Query[] = [];
		const downQueries: Query[] = [];
		upQueries.push(this.createViewSql(view));
		if (syncWithMetadata) upQueries.push(await this.insertViewDefinitionSql(view));
		downQueries.push(this.dropViewSql(view));
		if (syncWithMetadata) downQueries.push(await this.deleteViewDefinitionSql(view));
		await this.executeQueries(upQueries, downQueries);
	}

	/**
	 * Drops the view.
	 */
	async dropView(target: View | string): Promise<void> {
		const viewName = InstanceChecker.isView(target) ? target.name : target;
		const view = await this.getCachedView(viewName);

		const upQueries: Query[] = [];
		const downQueries: Query[] = [];
		upQueries.push(await this.deleteViewDefinitionSql(view));
		upQueries.push(this.dropViewSql(view));
		downQueries.push(await this.insertViewDefinitionSql(view));
		downQueries.push(this.createViewSql(view));
		await this.executeQueries(upQueries, downQueries);
	}

	/**
	 * Renames the given table.
	 */
	async renameTable(oldTableOrName: Table | string, newTableName: string): Promise<void> {
		const upQueries: Query[] = [];
		const downQueries: Query[] = [];
		const oldTable = InstanceChecker.isTable(oldTableOrName)
			? oldTableOrName
			: await this.getCachedTable(oldTableOrName);
		const newTable = oldTable.clone();

		const { schema: schemaName, tableName: oldTableName } = this.driver.parseTableName(oldTable);

		newTable.name = schemaName ? `${schemaName}.${newTableName}` : newTableName;

		upQueries.push(
			new Query(`ALTER TABLE ${this.escapePath(oldTable)} RENAME TO "${newTableName}"`),
		);
		downQueries.push(
			new Query(`ALTER TABLE ${this.escapePath(newTable)} RENAME TO "${oldTableName}"`),
		);

		// rename column primary key constraint if it has default constraint name
		if (
			newTable.primaryColumns.length > 0 &&
			!newTable.primaryColumns[0].primaryKeyConstraintName
		) {
			const columnNames = newTable.primaryColumns.map((column) => column.name);

			const oldPkName = this.connection.namingStrategy.primaryKeyName(oldTable, columnNames);

			const newPkName = this.connection.namingStrategy.primaryKeyName(newTable, columnNames);

			upQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(
						newTable,
					)} RENAME CONSTRAINT "${oldPkName}" TO "${newPkName}"`,
				),
			);
			downQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(
						newTable,
					)} RENAME CONSTRAINT "${newPkName}" TO "${oldPkName}"`,
				),
			);
		}

		// rename sequences
		newTable.columns.map((col) => {
			if (col.isGenerated && col.generationStrategy === 'increment') {
				const sequencePath = this.buildSequencePath(oldTable, col.name);
				const sequenceName = this.buildSequenceName(oldTable, col.name);

				const newSequencePath = this.buildSequencePath(newTable, col.name);
				const newSequenceName = this.buildSequenceName(newTable, col.name);

				const up = `ALTER SEQUENCE ${this.escapePath(sequencePath)} RENAME TO "${newSequenceName}"`;
				const down = `ALTER SEQUENCE ${this.escapePath(
					newSequencePath,
				)} RENAME TO "${sequenceName}"`;

				upQueries.push(new Query(up));
				downQueries.push(new Query(down));
			}
		});

		// rename unique constraints
		newTable.uniques.forEach((unique) => {
			const oldUniqueName = this.connection.namingStrategy.uniqueConstraintName(
				oldTable,
				unique.columnNames,
			);

			// Skip renaming if Unique has user defined constraint name
			if (unique.name !== oldUniqueName) return;

			// build new constraint name
			const newUniqueName = this.connection.namingStrategy.uniqueConstraintName(
				newTable,
				unique.columnNames,
			);

			// build queries
			upQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(newTable)} RENAME CONSTRAINT "${
						unique.name
					}" TO "${newUniqueName}"`,
				),
			);
			downQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(newTable)} RENAME CONSTRAINT "${newUniqueName}" TO "${
						unique.name
					}"`,
				),
			);

			// replace constraint name
			unique.name = newUniqueName;
		});

		// rename index constraints
		newTable.indices.forEach((index) => {
			const oldIndexName = this.connection.namingStrategy.indexName(
				oldTable,
				index.columnNames,
				index.where,
			);

			// Skip renaming if Index has user defined constraint name
			if (index.name !== oldIndexName) return;

			// build new constraint name
			const { schema } = this.driver.parseTableName(newTable);
			const newIndexName = this.connection.namingStrategy.indexName(
				newTable,
				index.columnNames,
				index.where,
			);

			// build queries
			const up = schema
				? `ALTER INDEX "${schema}"."${index.name}" RENAME TO "${newIndexName}"`
				: `ALTER INDEX "${index.name}" RENAME TO "${newIndexName}"`;
			const down = schema
				? `ALTER INDEX "${schema}"."${newIndexName}" RENAME TO "${index.name}"`
				: `ALTER INDEX "${newIndexName}" RENAME TO "${index.name}"`;
			upQueries.push(new Query(up));
			downQueries.push(new Query(down));

			// replace constraint name
			index.name = newIndexName;
		});

		// rename foreign key constraints
		newTable.foreignKeys.forEach((foreignKey) => {
			const oldForeignKeyName = this.connection.namingStrategy.foreignKeyName(
				oldTable,
				foreignKey.columnNames,
				this.getTablePath(foreignKey),
				foreignKey.referencedColumnNames,
			);

			// Skip renaming if foreign key has user defined constraint name
			if (foreignKey.name !== oldForeignKeyName) return;

			// build new constraint name
			const newForeignKeyName = this.connection.namingStrategy.foreignKeyName(
				newTable,
				foreignKey.columnNames,
				this.getTablePath(foreignKey),
				foreignKey.referencedColumnNames,
			);

			// build queries
			upQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(newTable)} RENAME CONSTRAINT "${
						foreignKey.name
					}" TO "${newForeignKeyName}"`,
				),
			);
			downQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(newTable)} RENAME CONSTRAINT "${newForeignKeyName}" TO "${
						foreignKey.name
					}"`,
				),
			);

			// replace constraint name
			foreignKey.name = newForeignKeyName;
		});

		// rename ENUM types
		const enumColumns = newTable.columns.filter(
			(column) => column.type === 'enum' || column.type === 'simple-enum',
		);
		for (let column of enumColumns) {
			// skip renaming for user-defined enum name
			if (column.enumName) continue;

			const oldEnumType = await this.getUserDefinedTypeName(oldTable, column);
			upQueries.push(
				new Query(
					`ALTER TYPE "${oldEnumType.schema}"."${oldEnumType.name}" RENAME TO ${this.buildEnumName(
						newTable,
						column,
						false,
					)}`,
				),
			);
			downQueries.push(
				new Query(
					`ALTER TYPE ${this.buildEnumName(newTable, column)} RENAME TO "${oldEnumType.name}"`,
				),
			);
		}
		await this.executeQueries(upQueries, downQueries);
	}

	/**
	 * Creates a new column from the column in the table.
	 */
	async addColumn(tableOrName: Table | string, column: TableColumn): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const clonedTable = table.clone();
		const upQueries: Query[] = [];
		const downQueries: Query[] = [];

		if (column.type === 'enum' || column.type === 'simple-enum') {
			const hasEnum = await this.hasEnumType(table, column);
			if (!hasEnum) {
				upQueries.push(this.createEnumTypeSql(table, column));
				downQueries.push(this.dropEnumTypeSql(table, column));
			}
		}

		upQueries.push(
			new Query(
				`ALTER TABLE ${this.escapePath(table)} ADD ${this.buildCreateColumnSql(table, column)}`,
			),
		);
		downQueries.push(
			new Query(`ALTER TABLE ${this.escapePath(table)} DROP COLUMN "${column.name}"`),
		);

		// create or update primary key constraint
		if (column.isPrimary) {
			const primaryColumns = clonedTable.primaryColumns;
			// if table already have primary key, me must drop it and recreate again
			if (primaryColumns.length > 0) {
				const pkName = primaryColumns[0].primaryKeyConstraintName
					? primaryColumns[0].primaryKeyConstraintName
					: this.connection.namingStrategy.primaryKeyName(
							clonedTable,
							primaryColumns.map((column) => column.name),
						);

				const columnNames = primaryColumns.map((column) => `"${column.name}"`).join(', ');

				upQueries.push(
					new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${pkName}"`),
				);
				downQueries.push(
					new Query(
						`ALTER TABLE ${this.escapePath(
							table,
						)} ADD CONSTRAINT "${pkName}" PRIMARY KEY (${columnNames})`,
					),
				);
			}

			primaryColumns.push(column);
			const pkName = primaryColumns[0].primaryKeyConstraintName
				? primaryColumns[0].primaryKeyConstraintName
				: this.connection.namingStrategy.primaryKeyName(
						clonedTable,
						primaryColumns.map((column) => column.name),
					);

			const columnNames = primaryColumns.map((column) => `"${column.name}"`).join(', ');

			upQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(
						table,
					)} ADD CONSTRAINT "${pkName}" PRIMARY KEY (${columnNames})`,
				),
			);
			downQueries.push(
				new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${pkName}"`),
			);
		}

		// create column index
		const columnIndex = clonedTable.indices.find(
			(index) => index.columnNames.length === 1 && index.columnNames[0] === column.name,
		);
		if (columnIndex) {
			upQueries.push(this.createIndexSql(table, columnIndex));
			downQueries.push(this.dropIndexSql(table, columnIndex));
		}

		// create unique constraint
		if (column.isUnique) {
			const uniqueConstraint = new TableUnique({
				name: this.connection.namingStrategy.uniqueConstraintName(table, [column.name]),
				columnNames: [column.name],
			});
			clonedTable.uniques.push(uniqueConstraint);
			upQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(table)} ADD CONSTRAINT "${
						uniqueConstraint.name
					}" UNIQUE ("${column.name}")`,
				),
			);
			downQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${uniqueConstraint.name}"`,
				),
			);
		}

		if (column.generatedType === 'STORED' && column.asExpression) {
			const tableNameWithSchema = (await this.getTableNameWithSchema(table.name)).split('.');
			const tableName = tableNameWithSchema[1];
			const schema = tableNameWithSchema[0];

			const insertQuery = this.insertTypeormMetadataSql({
				database: this.driver.database,
				schema,
				table: tableName,
				type: MetadataTableType.GENERATED_COLUMN,
				name: column.name,
				value: column.asExpression,
			});

			const deleteQuery = this.deleteTypeormMetadataSql({
				database: this.driver.database,
				schema,
				table: tableName,
				type: MetadataTableType.GENERATED_COLUMN,
				name: column.name,
			});

			upQueries.push(insertQuery);
			downQueries.push(deleteQuery);
		}

		// create column's comment
		if (column.comment) {
			upQueries.push(
				new Query(
					`COMMENT ON COLUMN ${this.escapePath(table)}."${
						column.name
					}" IS ${this.escapeComment(column.comment)}`,
				),
			);
			downQueries.push(
				new Query(
					`COMMENT ON COLUMN ${this.escapePath(table)}."${
						column.name
					}" IS ${this.escapeComment(column.comment)}`,
				),
			);
		}

		await this.executeQueries(upQueries, downQueries);

		clonedTable.addColumn(column);
		this.replaceCachedTable(table, clonedTable);
	}

	/**
	 * Creates a new columns from the column in the table.
	 */
	async addColumns(tableOrName: Table | string, columns: TableColumn[]): Promise<void> {
		for (const column of columns) {
			await this.addColumn(tableOrName, column);
		}
	}

	/**
	 * Renames column in the given table.
	 */
	async renameColumn(
		tableOrName: Table | string,
		oldTableColumnOrName: TableColumn | string,
		newTableColumnOrName: TableColumn | string,
	): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const oldColumn = InstanceChecker.isTableColumn(oldTableColumnOrName)
			? oldTableColumnOrName
			: table.columns.find((c) => c.name === oldTableColumnOrName);
		if (!oldColumn)
			throw new TypeORMError(
				`Column "${oldTableColumnOrName}" was not found in the "${table.name}" table.`,
			);

		let newColumn;
		if (InstanceChecker.isTableColumn(newTableColumnOrName)) {
			newColumn = newTableColumnOrName;
		} else {
			newColumn = oldColumn.clone();
			newColumn.name = newTableColumnOrName;
		}

		return this.changeColumn(table, oldColumn, newColumn);
	}

	/**
	 * Changes a column in the table.
	 */
	async changeColumn(
		tableOrName: Table | string,
		oldTableColumnOrName: TableColumn | string,
		newColumn: TableColumn,
	): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		let clonedTable = table.clone();
		const upQueries: Query[] = [];
		const downQueries: Query[] = [];
		let defaultValueChanged = false;

		const oldColumn = InstanceChecker.isTableColumn(oldTableColumnOrName)
			? oldTableColumnOrName
			: table.columns.find((column) => column.name === oldTableColumnOrName);
		if (!oldColumn)
			throw new TypeORMError(
				`Column "${oldTableColumnOrName}" was not found in the "${table.name}" table.`,
			);

		if (
			oldColumn.type !== newColumn.type ||
			oldColumn.length !== newColumn.length ||
			newColumn.isArray !== oldColumn.isArray ||
			(!oldColumn.generatedType && newColumn.generatedType === 'STORED') ||
			(oldColumn.asExpression !== newColumn.asExpression && newColumn.generatedType === 'STORED')
		) {
			// To avoid data conversion, we just recreate column
			await this.dropColumn(table, oldColumn);
			await this.addColumn(table, newColumn);

			// update cloned table
			clonedTable = table.clone();
		} else {
			if (oldColumn.name !== newColumn.name) {
				// rename column
				upQueries.push(
					new Query(
						`ALTER TABLE ${this.escapePath(table)} RENAME COLUMN "${
							oldColumn.name
						}" TO "${newColumn.name}"`,
					),
				);
				downQueries.push(
					new Query(
						`ALTER TABLE ${this.escapePath(table)} RENAME COLUMN "${
							newColumn.name
						}" TO "${oldColumn.name}"`,
					),
				);

				// rename ENUM type
				if (oldColumn.type === 'enum' || oldColumn.type === 'simple-enum') {
					const oldEnumType = await this.getUserDefinedTypeName(table, oldColumn);
					upQueries.push(
						new Query(
							`ALTER TYPE "${oldEnumType.schema}"."${
								oldEnumType.name
							}" RENAME TO ${this.buildEnumName(table, newColumn, false)}`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TYPE ${this.buildEnumName(table, newColumn)} RENAME TO "${oldEnumType.name}"`,
						),
					);
				}

				// rename column primary key constraint
				if (oldColumn.isPrimary === true && !oldColumn.primaryKeyConstraintName) {
					const primaryColumns = clonedTable.primaryColumns;

					// build old primary constraint name
					const columnNames = primaryColumns.map((column) => column.name);
					const oldPkName = this.connection.namingStrategy.primaryKeyName(clonedTable, columnNames);

					// replace old column name with new column name
					columnNames.splice(columnNames.indexOf(oldColumn.name), 1);
					columnNames.push(newColumn.name);

					// build new primary constraint name
					const newPkName = this.connection.namingStrategy.primaryKeyName(clonedTable, columnNames);

					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(
								table,
							)} RENAME CONSTRAINT "${oldPkName}" TO "${newPkName}"`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(
								table,
							)} RENAME CONSTRAINT "${newPkName}" TO "${oldPkName}"`,
						),
					);
				}

				// rename column sequence
				if (oldColumn.isGenerated === true && newColumn.generationStrategy === 'increment') {
					const sequencePath = this.buildSequencePath(table, oldColumn.name);
					const sequenceName = this.buildSequenceName(table, oldColumn.name);

					const newSequencePath = this.buildSequencePath(table, newColumn.name);
					const newSequenceName = this.buildSequenceName(table, newColumn.name);

					const up = `ALTER SEQUENCE ${this.escapePath(
						sequencePath,
					)} RENAME TO "${newSequenceName}"`;
					const down = `ALTER SEQUENCE ${this.escapePath(
						newSequencePath,
					)} RENAME TO "${sequenceName}"`;

					upQueries.push(new Query(up));
					downQueries.push(new Query(down));
				}

				// rename unique constraints
				clonedTable.findColumnUniques(oldColumn).forEach((unique) => {
					const oldUniqueName = this.connection.namingStrategy.uniqueConstraintName(
						clonedTable,
						unique.columnNames,
					);

					// Skip renaming if Unique has user defined constraint name
					if (unique.name !== oldUniqueName) return;

					// build new constraint name
					unique.columnNames.splice(unique.columnNames.indexOf(oldColumn.name), 1);
					unique.columnNames.push(newColumn.name);
					const newUniqueName = this.connection.namingStrategy.uniqueConstraintName(
						clonedTable,
						unique.columnNames,
					);

					// build queries
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} RENAME CONSTRAINT "${
								unique.name
							}" TO "${newUniqueName}"`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} RENAME CONSTRAINT "${newUniqueName}" TO "${
								unique.name
							}"`,
						),
					);

					// replace constraint name
					unique.name = newUniqueName;
				});

				// rename index constraints
				clonedTable.findColumnIndices(oldColumn).forEach((index) => {
					const oldIndexName = this.connection.namingStrategy.indexName(
						clonedTable,
						index.columnNames,
						index.where,
					);

					// Skip renaming if Index has user defined constraint name
					if (index.name !== oldIndexName) return;

					// build new constraint name
					index.columnNames.splice(index.columnNames.indexOf(oldColumn.name), 1);
					index.columnNames.push(newColumn.name);
					const { schema } = this.driver.parseTableName(table);
					const newIndexName = this.connection.namingStrategy.indexName(
						clonedTable,
						index.columnNames,
						index.where,
					);

					// build queries
					const up = schema
						? `ALTER INDEX "${schema}"."${index.name}" RENAME TO "${newIndexName}"`
						: `ALTER INDEX "${index.name}" RENAME TO "${newIndexName}"`;
					const down = schema
						? `ALTER INDEX "${schema}"."${newIndexName}" RENAME TO "${index.name}"`
						: `ALTER INDEX "${newIndexName}" RENAME TO "${index.name}"`;

					upQueries.push(new Query(up));
					downQueries.push(new Query(down));

					// replace constraint name
					index.name = newIndexName;
				});

				// rename foreign key constraints
				clonedTable.findColumnForeignKeys(oldColumn).forEach((foreignKey) => {
					const foreignKeyName = this.connection.namingStrategy.foreignKeyName(
						clonedTable,
						foreignKey.columnNames,
						this.getTablePath(foreignKey),
						foreignKey.referencedColumnNames,
					);

					// Skip renaming if foreign key has user defined constraint name
					if (foreignKey.name !== foreignKeyName) return;

					// build new constraint name
					foreignKey.columnNames.splice(foreignKey.columnNames.indexOf(oldColumn.name), 1);
					foreignKey.columnNames.push(newColumn.name);
					const newForeignKeyName = this.connection.namingStrategy.foreignKeyName(
						clonedTable,
						foreignKey.columnNames,
						this.getTablePath(foreignKey),
						foreignKey.referencedColumnNames,
					);

					// build queries
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} RENAME CONSTRAINT "${
								foreignKey.name
							}" TO "${newForeignKeyName}"`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} RENAME CONSTRAINT "${newForeignKeyName}" TO "${
								foreignKey.name
							}"`,
						),
					);

					// replace constraint name
					foreignKey.name = newForeignKeyName;
				});

				// rename old column in the Table object
				const oldTableColumn = clonedTable.columns.find((column) => column.name === oldColumn.name);
				clonedTable.columns[clonedTable.columns.indexOf(oldTableColumn!)].name = newColumn.name;
				oldColumn.name = newColumn.name;
			}

			if (newColumn.precision !== oldColumn.precision || newColumn.scale !== oldColumn.scale) {
				upQueries.push(
					new Query(
						`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
							newColumn.name
						}" TYPE ${this.driver.createFullType(newColumn)}`,
					),
				);
				downQueries.push(
					new Query(
						`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
							newColumn.name
						}" TYPE ${this.driver.createFullType(oldColumn)}`,
					),
				);
			}

			if (
				(newColumn.type === 'enum' || newColumn.type === 'simple-enum') &&
				(oldColumn.type === 'enum' || oldColumn.type === 'simple-enum') &&
				(!OrmUtils.isArraysEqual(newColumn.enum!, oldColumn.enum!) ||
					newColumn.enumName !== oldColumn.enumName)
			) {
				const arraySuffix = newColumn.isArray ? '[]' : '';

				// "public"."new_enum"
				const newEnumName = this.buildEnumName(table, newColumn);

				// "public"."old_enum"
				const oldEnumName = this.buildEnumName(table, oldColumn);

				// "old_enum"
				const oldEnumNameWithoutSchema = this.buildEnumName(table, oldColumn, false);

				//"public"."old_enum_old"
				const oldEnumNameWithSchema_old = this.buildEnumName(table, oldColumn, true, false, true);

				//"old_enum_old"
				const oldEnumNameWithoutSchema_old = this.buildEnumName(
					table,
					oldColumn,
					false,
					false,
					true,
				);

				// rename old ENUM
				upQueries.push(
					new Query(`ALTER TYPE ${oldEnumName} RENAME TO ${oldEnumNameWithoutSchema_old}`),
				);
				downQueries.push(
					new Query(
						`ALTER TYPE ${oldEnumNameWithSchema_old} RENAME TO ${oldEnumNameWithoutSchema}`,
					),
				);

				// create new ENUM
				upQueries.push(this.createEnumTypeSql(table, newColumn, newEnumName));
				downQueries.push(this.dropEnumTypeSql(table, newColumn, newEnumName));

				// if column have default value, we must drop it to avoid issues with type casting
				if (oldColumn.default !== null && oldColumn.default !== undefined) {
					// mark default as changed to prevent double update
					defaultValueChanged = true;
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${oldColumn.name}" DROP DEFAULT`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${oldColumn.name}" SET DEFAULT ${
								oldColumn.default
							}`,
						),
					);
				}

				// build column types
				const upType = `${newEnumName}${arraySuffix} USING "${newColumn.name}"::"text"::${newEnumName}${arraySuffix}`;
				const downType = `${oldEnumNameWithSchema_old}${arraySuffix} USING "${newColumn.name}"::"text"::${oldEnumNameWithSchema_old}${arraySuffix}`;

				// update column to use new type
				upQueries.push(
					new Query(
						`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${newColumn.name}" TYPE ${upType}`,
					),
				);
				downQueries.push(
					new Query(
						`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
							newColumn.name
						}" TYPE ${downType}`,
					),
				);

				// restore column default or create new one
				if (newColumn.default !== null && newColumn.default !== undefined) {
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${newColumn.name}" SET DEFAULT ${
								newColumn.default
							}`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${newColumn.name}" DROP DEFAULT`,
						),
					);
				}

				// remove old ENUM
				upQueries.push(this.dropEnumTypeSql(table, oldColumn, oldEnumNameWithSchema_old));
				downQueries.push(this.createEnumTypeSql(table, oldColumn, oldEnumNameWithSchema_old));
			}

			if (oldColumn.isNullable !== newColumn.isNullable) {
				if (newColumn.isNullable) {
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(
								table,
							)} ALTER COLUMN "${oldColumn.name}" DROP NOT NULL`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${oldColumn.name}" SET NOT NULL`,
						),
					);
				} else {
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${oldColumn.name}" SET NOT NULL`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(
								table,
							)} ALTER COLUMN "${oldColumn.name}" DROP NOT NULL`,
						),
					);
				}
			}

			if (oldColumn.comment !== newColumn.comment) {
				upQueries.push(
					new Query(
						`COMMENT ON COLUMN ${this.escapePath(table)}."${
							oldColumn.name
						}" IS ${this.escapeComment(newColumn.comment)}`,
					),
				);
				downQueries.push(
					new Query(
						`COMMENT ON COLUMN ${this.escapePath(table)}."${
							newColumn.name
						}" IS ${this.escapeComment(oldColumn.comment)}`,
					),
				);
			}

			if (newColumn.isPrimary !== oldColumn.isPrimary) {
				const primaryColumns = clonedTable.primaryColumns;

				// if primary column state changed, we must always drop existed constraint.
				if (primaryColumns.length > 0) {
					const pkName = primaryColumns[0].primaryKeyConstraintName
						? primaryColumns[0].primaryKeyConstraintName
						: this.connection.namingStrategy.primaryKeyName(
								clonedTable,
								primaryColumns.map((column) => column.name),
							);

					const columnNames = primaryColumns.map((column) => `"${column.name}"`).join(', ');

					upQueries.push(
						new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${pkName}"`),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(
								table,
							)} ADD CONSTRAINT "${pkName}" PRIMARY KEY (${columnNames})`,
						),
					);
				}

				if (newColumn.isPrimary === true) {
					primaryColumns.push(newColumn);
					// update column in table
					const column = clonedTable.columns.find((column) => column.name === newColumn.name);
					column!.isPrimary = true;
					const pkName = primaryColumns[0].primaryKeyConstraintName
						? primaryColumns[0].primaryKeyConstraintName
						: this.connection.namingStrategy.primaryKeyName(
								clonedTable,
								primaryColumns.map((column) => column.name),
							);

					const columnNames = primaryColumns.map((column) => `"${column.name}"`).join(', ');

					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(
								table,
							)} ADD CONSTRAINT "${pkName}" PRIMARY KEY (${columnNames})`,
						),
					);
					downQueries.push(
						new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${pkName}"`),
					);
				} else {
					const primaryColumn = primaryColumns.find((c) => c.name === newColumn.name);
					primaryColumns.splice(primaryColumns.indexOf(primaryColumn!), 1);

					// update column in table
					const column = clonedTable.columns.find((column) => column.name === newColumn.name);
					column!.isPrimary = false;

					// if we have another primary keys, we must recreate constraint.
					if (primaryColumns.length > 0) {
						const pkName = primaryColumns[0].primaryKeyConstraintName
							? primaryColumns[0].primaryKeyConstraintName
							: this.connection.namingStrategy.primaryKeyName(
									clonedTable,
									primaryColumns.map((column) => column.name),
								);

						const columnNames = primaryColumns.map((column) => `"${column.name}"`).join(', ');

						upQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(
									table,
								)} ADD CONSTRAINT "${pkName}" PRIMARY KEY (${columnNames})`,
							),
						);
						downQueries.push(
							new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${pkName}"`),
						);
					}
				}
			}

			if (newColumn.isUnique !== oldColumn.isUnique) {
				if (newColumn.isUnique === true) {
					const uniqueConstraint = new TableUnique({
						name: this.connection.namingStrategy.uniqueConstraintName(table, [newColumn.name]),
						columnNames: [newColumn.name],
					});
					clonedTable.uniques.push(uniqueConstraint);
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ADD CONSTRAINT "${
								uniqueConstraint.name
							}" UNIQUE ("${newColumn.name}")`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${uniqueConstraint.name}"`,
						),
					);
				} else {
					const uniqueConstraint = clonedTable.uniques.find((unique) => {
						return (
							unique.columnNames.length === 1 &&
							!!unique.columnNames.find((columnName) => columnName === newColumn.name)
						);
					});
					clonedTable.uniques.splice(clonedTable.uniques.indexOf(uniqueConstraint!), 1);
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${uniqueConstraint!.name}"`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ADD CONSTRAINT "${
								uniqueConstraint!.name
							}" UNIQUE ("${newColumn.name}")`,
						),
					);
				}
			}

			if (oldColumn.isGenerated !== newColumn.isGenerated) {
				// if old column was "generated", we should clear defaults
				if (oldColumn.isGenerated) {
					if (oldColumn.generationStrategy === 'uuid') {
						upQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									oldColumn.name
								}" DROP DEFAULT`,
							),
						);
						downQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									oldColumn.name
								}" SET DEFAULT ${this.driver.uuidGenerator}`,
							),
						);
					} else if (oldColumn.generationStrategy === 'increment') {
						upQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" DROP DEFAULT`,
							),
						);
						downQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" SET DEFAULT nextval('${this.escapePath(
									this.buildSequencePath(table, newColumn),
								)}')`,
							),
						);

						upQueries.push(
							new Query(
								`DROP SEQUENCE ${this.escapePath(this.buildSequencePath(table, newColumn))}`,
							),
						);
						downQueries.push(
							new Query(
								`CREATE SEQUENCE IF NOT EXISTS ${this.escapePath(
									this.buildSequencePath(table, newColumn),
								)} OWNED BY ${this.escapePath(table)}."${newColumn.name}"`,
							),
						);
					}
				}

				if (newColumn.generationStrategy === 'uuid') {
					if (newColumn.isGenerated === true) {
						upQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" SET DEFAULT ${this.driver.uuidGenerator}`,
							),
						);
						downQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" DROP DEFAULT`,
							),
						);
					} else {
						upQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" DROP DEFAULT`,
							),
						);
						downQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" SET DEFAULT ${this.driver.uuidGenerator}`,
							),
						);
					}
				} else if (newColumn.generationStrategy === 'increment') {
					if (newColumn.isGenerated === true) {
						upQueries.push(
							new Query(
								`CREATE SEQUENCE IF NOT EXISTS ${this.escapePath(
									this.buildSequencePath(table, newColumn),
								)} OWNED BY ${this.escapePath(table)}."${newColumn.name}"`,
							),
						);
						downQueries.push(
							new Query(
								`DROP SEQUENCE ${this.escapePath(this.buildSequencePath(table, newColumn))}`,
							),
						);

						upQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" SET DEFAULT nextval('${this.escapePath(
									this.buildSequencePath(table, newColumn),
								)}')`,
							),
						);
						downQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" DROP DEFAULT`,
							),
						);
					} else {
						upQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" DROP DEFAULT`,
							),
						);
						downQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" SET DEFAULT nextval('${this.escapePath(
									this.buildSequencePath(table, newColumn),
								)}')`,
							),
						);

						upQueries.push(
							new Query(
								`DROP SEQUENCE ${this.escapePath(this.buildSequencePath(table, newColumn))}`,
							),
						);
						downQueries.push(
							new Query(
								`CREATE SEQUENCE IF NOT EXISTS ${this.escapePath(
									this.buildSequencePath(table, newColumn),
								)} OWNED BY ${this.escapePath(table)}."${newColumn.name}"`,
							),
						);
					}
				}
			}

			// the default might have changed when the enum changed
			if (newColumn.default !== oldColumn.default && !defaultValueChanged) {
				if (newColumn.default !== null && newColumn.default !== undefined) {
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${newColumn.name}" SET DEFAULT ${
								newColumn.default
							}`,
						),
					);

					if (oldColumn.default !== null && oldColumn.default !== undefined) {
						downQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" SET DEFAULT ${oldColumn.default}`,
							),
						);
					} else {
						downQueries.push(
							new Query(
								`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
									newColumn.name
								}" DROP DEFAULT`,
							),
						);
					}
				} else if (oldColumn.default !== null && oldColumn.default !== undefined) {
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${newColumn.name}" DROP DEFAULT`,
						),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${newColumn.name}" SET DEFAULT ${
								oldColumn.default
							}`,
						),
					);
				}
			}

			if (
				(newColumn.spatialFeatureType || '').toLowerCase() !==
					(oldColumn.spatialFeatureType || '').toLowerCase() ||
				newColumn.srid !== oldColumn.srid
			) {
				upQueries.push(
					new Query(
						`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
							newColumn.name
						}" TYPE ${this.driver.createFullType(newColumn)}`,
					),
				);
				downQueries.push(
					new Query(
						`ALTER TABLE ${this.escapePath(table)} ALTER COLUMN "${
							newColumn.name
						}" TYPE ${this.driver.createFullType(oldColumn)}`,
					),
				);
			}

			if (newColumn.generatedType !== oldColumn.generatedType) {
				// Convert generated column data to normal column
				if (!newColumn.generatedType || newColumn.generatedType === 'VIRTUAL') {
					// We can copy the generated data to the new column
					const tableNameWithSchema = (await this.getTableNameWithSchema(table.name)).split('.');
					const tableName = tableNameWithSchema[1];
					const schema = tableNameWithSchema[0];

					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(
								table,
							)} RENAME COLUMN "${oldColumn.name}" TO "TEMP_OLD_${oldColumn.name}"`,
						),
					);
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ADD ${this.buildCreateColumnSql(
								table,
								newColumn,
							)}`,
						),
					);
					upQueries.push(
						new Query(
							`UPDATE ${this.escapePath(table)} SET "${
								newColumn.name
							}" = "TEMP_OLD_${oldColumn.name}"`,
						),
					);
					upQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} DROP COLUMN "TEMP_OLD_${oldColumn.name}"`,
						),
					);
					upQueries.push(
						this.deleteTypeormMetadataSql({
							database: this.driver.database,
							schema,
							table: tableName,
							type: MetadataTableType.GENERATED_COLUMN,
							name: oldColumn.name,
						}),
					);
					// However, we can't copy it back on downgrade. It needs to regenerate.
					downQueries.push(
						this.insertTypeormMetadataSql({
							database: this.driver.database,
							schema,
							table: tableName,
							type: MetadataTableType.GENERATED_COLUMN,
							name: oldColumn.name,
							value: oldColumn.asExpression,
						}),
					);
					downQueries.push(
						new Query(
							`ALTER TABLE ${this.escapePath(table)} ADD ${this.buildCreateColumnSql(
								table,
								oldColumn,
							)}`,
						),
					);
					downQueries.push(
						new Query(`ALTER TABLE ${this.escapePath(table)} DROP COLUMN "${newColumn.name}"`),
					);
					// downQueries.push(
					//     this.deleteTypeormMetadataSql({
					//         database: this.driver.database,
					//         schema,
					//         table: tableName,
					//         type: MetadataTableType.GENERATED_COLUMN,
					//         name: newColumn.name,
					//     }),
					// )
				}
			}
		}

		await this.executeQueries(upQueries, downQueries);
		this.replaceCachedTable(table, clonedTable);
	}

	/**
	 * Changes a column in the table.
	 */
	async changeColumns(
		tableOrName: Table | string,
		changedColumns: { newColumn: TableColumn; oldColumn: TableColumn }[],
	): Promise<void> {
		for (const { oldColumn, newColumn } of changedColumns) {
			await this.changeColumn(tableOrName, oldColumn, newColumn);
		}
	}

	/**
	 * Drops column in the table.
	 */
	async dropColumn(tableOrName: Table | string, columnOrName: TableColumn | string): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const column = InstanceChecker.isTableColumn(columnOrName)
			? columnOrName
			: table.findColumnByName(columnOrName);
		if (!column)
			throw new TypeORMError(`Column "${columnOrName}" was not found in table "${table.name}"`);

		const clonedTable = table.clone();
		const upQueries: Query[] = [];
		const downQueries: Query[] = [];

		// drop primary key constraint
		if (column.isPrimary) {
			const pkName = column.primaryKeyConstraintName
				? column.primaryKeyConstraintName
				: this.connection.namingStrategy.primaryKeyName(
						clonedTable,
						clonedTable.primaryColumns.map((column) => column.name),
					);

			const columnNames = clonedTable.primaryColumns
				.map((primaryColumn) => `"${primaryColumn.name}"`)
				.join(', ');

			upQueries.push(
				new Query(`ALTER TABLE ${this.escapePath(clonedTable)} DROP CONSTRAINT "${pkName}"`),
			);
			downQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(
						clonedTable,
					)} ADD CONSTRAINT "${pkName}" PRIMARY KEY (${columnNames})`,
				),
			);

			// update column in table
			const tableColumn = clonedTable.findColumnByName(column.name);
			tableColumn!.isPrimary = false;

			// if primary key have multiple columns, we must recreate it without dropped column
			if (clonedTable.primaryColumns.length > 0) {
				const pkName = clonedTable.primaryColumns[0].primaryKeyConstraintName
					? clonedTable.primaryColumns[0].primaryKeyConstraintName
					: this.connection.namingStrategy.primaryKeyName(
							clonedTable,
							clonedTable.primaryColumns.map((column) => column.name),
						);

				const columnNames = clonedTable.primaryColumns
					.map((primaryColumn) => `"${primaryColumn.name}"`)
					.join(', ');

				upQueries.push(
					new Query(
						`ALTER TABLE ${this.escapePath(
							clonedTable,
						)} ADD CONSTRAINT "${pkName}" PRIMARY KEY (${columnNames})`,
					),
				);
				downQueries.push(
					new Query(`ALTER TABLE ${this.escapePath(clonedTable)} DROP CONSTRAINT "${pkName}"`),
				);
			}
		}

		// drop column index
		const columnIndex = clonedTable.indices.find(
			(index) => index.columnNames.length === 1 && index.columnNames[0] === column.name,
		);
		if (columnIndex) {
			clonedTable.indices.splice(clonedTable.indices.indexOf(columnIndex), 1);
			upQueries.push(this.dropIndexSql(table, columnIndex));
			downQueries.push(this.createIndexSql(table, columnIndex));
		}

		// drop column check
		const columnCheck = clonedTable.checks.find(
			(check) =>
				!!check.columnNames &&
				check.columnNames.length === 1 &&
				check.columnNames[0] === column.name,
		);
		if (columnCheck) {
			clonedTable.checks.splice(clonedTable.checks.indexOf(columnCheck), 1);
			upQueries.push(this.dropCheckConstraintSql(table, columnCheck));
			downQueries.push(this.createCheckConstraintSql(table, columnCheck));
		}

		// drop column unique
		const columnUnique = clonedTable.uniques.find(
			(unique) => unique.columnNames.length === 1 && unique.columnNames[0] === column.name,
		);
		if (columnUnique) {
			clonedTable.uniques.splice(clonedTable.uniques.indexOf(columnUnique), 1);
			upQueries.push(this.dropUniqueConstraintSql(table, columnUnique));
			downQueries.push(this.createUniqueConstraintSql(table, columnUnique));
		}

		upQueries.push(new Query(`ALTER TABLE ${this.escapePath(table)} DROP COLUMN "${column.name}"`));
		downQueries.push(
			new Query(
				`ALTER TABLE ${this.escapePath(table)} ADD ${this.buildCreateColumnSql(table, column)}`,
			),
		);

		// drop enum type
		if (column.type === 'enum' || column.type === 'simple-enum') {
			const hasEnum = await this.hasEnumType(table, column);
			if (hasEnum) {
				const enumType = await this.getUserDefinedTypeName(table, column);
				const escapedEnumName = `"${enumType.schema}"."${enumType.name}"`;
				upQueries.push(this.dropEnumTypeSql(table, column, escapedEnumName));
				downQueries.push(this.createEnumTypeSql(table, column, escapedEnumName));
			}
		}

		if (column.generatedType === 'STORED') {
			const tableNameWithSchema = (await this.getTableNameWithSchema(table.name)).split('.');
			const tableName = tableNameWithSchema[1];
			const schema = tableNameWithSchema[0];
			const deleteQuery = this.deleteTypeormMetadataSql({
				database: this.driver.database,
				schema,
				table: tableName,
				type: MetadataTableType.GENERATED_COLUMN,
				name: column.name,
			});
			const insertQuery = this.insertTypeormMetadataSql({
				database: this.driver.database,
				schema,
				table: tableName,
				type: MetadataTableType.GENERATED_COLUMN,
				name: column.name,
				value: column.asExpression,
			});

			upQueries.push(deleteQuery);
			downQueries.push(insertQuery);
		}

		await this.executeQueries(upQueries, downQueries);

		clonedTable.removeColumn(column);
		this.replaceCachedTable(table, clonedTable);
	}

	/**
	 * Drops the columns in the table.
	 */
	async dropColumns(tableOrName: Table | string, columns: TableColumn[] | string[]): Promise<void> {
		for (const column of columns) {
			await this.dropColumn(tableOrName, column);
		}
	}

	/**
	 * Creates a new primary key.
	 */
	async createPrimaryKey(
		tableOrName: Table | string,
		columnNames: string[],
		constraintName?: string,
	): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const clonedTable = table.clone();

		const up = this.createPrimaryKeySql(table, columnNames, constraintName);

		// mark columns as primary, because dropPrimaryKeySql build constraint name from table primary column names.
		clonedTable.columns.forEach((column) => {
			if (columnNames.find((columnName) => columnName === column.name)) column.isPrimary = true;
		});
		const down = this.dropPrimaryKeySql(clonedTable);

		await this.executeQueries(up, down);
		this.replaceCachedTable(table, clonedTable);
	}

	/**
	 * Updates composite primary keys.
	 */
	async updatePrimaryKeys(tableOrName: Table | string, columns: TableColumn[]): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const clonedTable = table.clone();
		const columnNames = columns.map((column) => column.name);
		const upQueries: Query[] = [];
		const downQueries: Query[] = [];

		// if table already have primary columns, we must drop them.
		const primaryColumns = clonedTable.primaryColumns;
		if (primaryColumns.length > 0) {
			const pkName = primaryColumns[0].primaryKeyConstraintName
				? primaryColumns[0].primaryKeyConstraintName
				: this.connection.namingStrategy.primaryKeyName(
						clonedTable,
						primaryColumns.map((column) => column.name),
					);

			const columnNamesString = primaryColumns.map((column) => `"${column.name}"`).join(', ');

			upQueries.push(
				new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${pkName}"`),
			);
			downQueries.push(
				new Query(
					`ALTER TABLE ${this.escapePath(
						table,
					)} ADD CONSTRAINT "${pkName}" PRIMARY KEY (${columnNamesString})`,
				),
			);
		}

		// update columns in table.
		clonedTable.columns
			.filter((column) => columnNames.indexOf(column.name) !== -1)
			.forEach((column) => (column.isPrimary = true));

		const pkName = primaryColumns[0]?.primaryKeyConstraintName
			? primaryColumns[0].primaryKeyConstraintName
			: this.connection.namingStrategy.primaryKeyName(clonedTable, columnNames);

		const columnNamesString = columnNames.map((columnName) => `"${columnName}"`).join(', ');

		upQueries.push(
			new Query(
				`ALTER TABLE ${this.escapePath(
					table,
				)} ADD CONSTRAINT "${pkName}" PRIMARY KEY (${columnNamesString})`,
			),
		);
		downQueries.push(
			new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${pkName}"`),
		);

		await this.executeQueries(upQueries, downQueries);
		this.replaceCachedTable(table, clonedTable);
	}

	/**
	 * Drops a primary key.
	 */
	async dropPrimaryKey(tableOrName: Table | string, constraintName?: string): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const up = this.dropPrimaryKeySql(table);
		const down = this.createPrimaryKeySql(
			table,
			table.primaryColumns.map((column) => column.name),
			constraintName,
		);
		await this.executeQueries(up, down);
		table.primaryColumns.forEach((column) => {
			column.isPrimary = false;
		});
	}

	/**
	 * Creates new unique constraint.
	 */
	async createUniqueConstraint(
		tableOrName: Table | string,
		uniqueConstraint: TableUnique,
	): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);

		// new unique constraint may be passed without name. In this case we generate unique name manually.
		if (!uniqueConstraint.name)
			uniqueConstraint.name = this.connection.namingStrategy.uniqueConstraintName(
				table,
				uniqueConstraint.columnNames,
			);

		const up = this.createUniqueConstraintSql(table, uniqueConstraint);
		const down = this.dropUniqueConstraintSql(table, uniqueConstraint);
		await this.executeQueries(up, down);
		table.addUniqueConstraint(uniqueConstraint);
	}

	/**
	 * Creates new unique constraints.
	 */
	async createUniqueConstraints(
		tableOrName: Table | string,
		uniqueConstraints: TableUnique[],
	): Promise<void> {
		for (const uniqueConstraint of uniqueConstraints) {
			await this.createUniqueConstraint(tableOrName, uniqueConstraint);
		}
	}

	/**
	 * Drops unique constraint.
	 */
	async dropUniqueConstraint(
		tableOrName: Table | string,
		uniqueOrName: TableUnique | string,
	): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const uniqueConstraint = InstanceChecker.isTableUnique(uniqueOrName)
			? uniqueOrName
			: table.uniques.find((u) => u.name === uniqueOrName);
		if (!uniqueConstraint)
			throw new TypeORMError(`Supplied unique constraint was not found in table ${table.name}`);

		const up = this.dropUniqueConstraintSql(table, uniqueConstraint);
		const down = this.createUniqueConstraintSql(table, uniqueConstraint);
		await this.executeQueries(up, down);
		table.removeUniqueConstraint(uniqueConstraint);
	}

	/**
	 * Drops unique constraints.
	 */
	async dropUniqueConstraints(
		tableOrName: Table | string,
		uniqueConstraints: TableUnique[],
	): Promise<void> {
		for (const uniqueConstraint of uniqueConstraints) {
			await this.dropUniqueConstraint(tableOrName, uniqueConstraint);
		}
	}

	/**
	 * Creates new check constraint.
	 */
	async createCheckConstraint(
		tableOrName: Table | string,
		checkConstraint: TableCheck,
	): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);

		// new unique constraint may be passed without name. In this case we generate unique name manually.
		if (!checkConstraint.name)
			checkConstraint.name = this.connection.namingStrategy.checkConstraintName(
				table,
				checkConstraint.expression!,
			);

		const up = this.createCheckConstraintSql(table, checkConstraint);
		const down = this.dropCheckConstraintSql(table, checkConstraint);
		await this.executeQueries(up, down);
		table.addCheckConstraint(checkConstraint);
	}

	/**
	 * Creates new check constraints.
	 */
	async createCheckConstraints(
		tableOrName: Table | string,
		checkConstraints: TableCheck[],
	): Promise<void> {
		const promises = checkConstraints.map((checkConstraint) =>
			this.createCheckConstraint(tableOrName, checkConstraint),
		);
		await Promise.all(promises);
	}

	/**
	 * Drops check constraint.
	 */
	async dropCheckConstraint(
		tableOrName: Table | string,
		checkOrName: TableCheck | string,
	): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const checkConstraint = InstanceChecker.isTableCheck(checkOrName)
			? checkOrName
			: table.checks.find((c) => c.name === checkOrName);
		if (!checkConstraint)
			throw new TypeORMError(`Supplied check constraint was not found in table ${table.name}`);

		const up = this.dropCheckConstraintSql(table, checkConstraint);
		const down = this.createCheckConstraintSql(table, checkConstraint);
		await this.executeQueries(up, down);
		table.removeCheckConstraint(checkConstraint);
	}

	/**
	 * Drops check constraints.
	 */
	async dropCheckConstraints(
		tableOrName: Table | string,
		checkConstraints: TableCheck[],
	): Promise<void> {
		const promises = checkConstraints.map((checkConstraint) =>
			this.dropCheckConstraint(tableOrName, checkConstraint),
		);
		await Promise.all(promises);
	}

	/**
	 * Creates new exclusion constraint.
	 */
	async createExclusionConstraint(
		tableOrName: Table | string,
		exclusionConstraint: TableExclusion,
	): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);

		// new unique constraint may be passed without name. In this case we generate unique name manually.
		if (!exclusionConstraint.name)
			exclusionConstraint.name = this.connection.namingStrategy.exclusionConstraintName(
				table,
				exclusionConstraint.expression!,
			);

		const up = this.createExclusionConstraintSql(table, exclusionConstraint);
		const down = this.dropExclusionConstraintSql(table, exclusionConstraint);
		await this.executeQueries(up, down);
		table.addExclusionConstraint(exclusionConstraint);
	}

	/**
	 * Creates new exclusion constraints.
	 */
	async createExclusionConstraints(
		tableOrName: Table | string,
		exclusionConstraints: TableExclusion[],
	): Promise<void> {
		const promises = exclusionConstraints.map((exclusionConstraint) =>
			this.createExclusionConstraint(tableOrName, exclusionConstraint),
		);
		await Promise.all(promises);
	}

	/**
	 * Drops exclusion constraint.
	 */
	async dropExclusionConstraint(
		tableOrName: Table | string,
		exclusionOrName: TableExclusion | string,
	): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const exclusionConstraint = InstanceChecker.isTableExclusion(exclusionOrName)
			? exclusionOrName
			: table.exclusions.find((c) => c.name === exclusionOrName);
		if (!exclusionConstraint)
			throw new TypeORMError(`Supplied exclusion constraint was not found in table ${table.name}`);

		const up = this.dropExclusionConstraintSql(table, exclusionConstraint);
		const down = this.createExclusionConstraintSql(table, exclusionConstraint);
		await this.executeQueries(up, down);
		table.removeExclusionConstraint(exclusionConstraint);
	}

	/**
	 * Drops exclusion constraints.
	 */
	async dropExclusionConstraints(
		tableOrName: Table | string,
		exclusionConstraints: TableExclusion[],
	): Promise<void> {
		const promises = exclusionConstraints.map((exclusionConstraint) =>
			this.dropExclusionConstraint(tableOrName, exclusionConstraint),
		);
		await Promise.all(promises);
	}

	/**
	 * Creates a new foreign key.
	 */
	async createForeignKey(tableOrName: Table | string, foreignKey: TableForeignKey): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);

		// new FK may be passed without name. In this case we generate FK name manually.
		if (!foreignKey.name)
			foreignKey.name = this.connection.namingStrategy.foreignKeyName(
				table,
				foreignKey.columnNames,
				this.getTablePath(foreignKey),
				foreignKey.referencedColumnNames,
			);

		const up = this.createForeignKeySql(table, foreignKey);
		const down = this.dropForeignKeySql(table, foreignKey);
		await this.executeQueries(up, down);
		table.addForeignKey(foreignKey);
	}

	/**
	 * Creates a new foreign keys.
	 */
	async createForeignKeys(
		tableOrName: Table | string,
		foreignKeys: TableForeignKey[],
	): Promise<void> {
		for (const foreignKey of foreignKeys) {
			await this.createForeignKey(tableOrName, foreignKey);
		}
	}

	/**
	 * Drops a foreign key from the table.
	 */
	async dropForeignKey(
		tableOrName: Table | string,
		foreignKeyOrName: TableForeignKey | string,
	): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const foreignKey = InstanceChecker.isTableForeignKey(foreignKeyOrName)
			? foreignKeyOrName
			: table.foreignKeys.find((fk) => fk.name === foreignKeyOrName);
		if (!foreignKey)
			throw new TypeORMError(`Supplied foreign key was not found in table ${table.name}`);

		if (!foreignKey.name) {
			foreignKey.name = this.connection.namingStrategy.foreignKeyName(
				table,
				foreignKey.columnNames,
				this.getTablePath(foreignKey),
				foreignKey.referencedColumnNames,
			);
		}

		const up = this.dropForeignKeySql(table, foreignKey);
		const down = this.createForeignKeySql(table, foreignKey);
		await this.executeQueries(up, down);
		table.removeForeignKey(foreignKey);
	}

	/**
	 * Drops a foreign keys from the table.
	 */
	async dropForeignKeys(
		tableOrName: Table | string,
		foreignKeys: TableForeignKey[],
	): Promise<void> {
		for (const foreignKey of foreignKeys) {
			await this.dropForeignKey(tableOrName, foreignKey);
		}
	}

	/**
	 * Creates a new index.
	 */
	async createIndex(tableOrName: Table | string, index: TableIndex): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);

		// new index may be passed without name. In this case we generate index name manually.
		if (!index.name) index.name = this.generateIndexName(table, index);

		const up = this.createIndexSql(table, index);
		const down = this.dropIndexSql(table, index);
		await this.executeQueries(up, down);
		table.addIndex(index);
	}

	/**
	 * Create a new view index.
	 */
	async createViewIndex(viewOrName: View | string, index: TableIndex): Promise<void> {
		const view = InstanceChecker.isView(viewOrName)
			? viewOrName
			: await this.getCachedView(viewOrName);

		// new index may be passed without name. In this case we generate index name manually.
		if (!index.name) index.name = this.generateIndexName(view, index);

		const up = this.createViewIndexSql(view, index);
		const down = this.dropIndexSql(view, index);
		await this.executeQueries(up, down);
		view.addIndex(index);
	}

	/**
	 * Creates a new indices
	 */
	async createIndices(tableOrName: Table | string, indices: TableIndex[]): Promise<void> {
		for (const index of indices) {
			await this.createIndex(tableOrName, index);
		}
	}

	/**
	 * Creates new view indices
	 */
	async createViewIndices(viewOrName: View | string, indices: TableIndex[]): Promise<void> {
		for (const index of indices) {
			await this.createViewIndex(viewOrName, index);
		}
	}

	/**
	 * Drops an index from the table.
	 */
	async dropIndex(tableOrName: Table | string, indexOrName: TableIndex | string): Promise<void> {
		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);
		const index = InstanceChecker.isTableIndex(indexOrName)
			? indexOrName
			: table.indices.find((i) => i.name === indexOrName);
		if (!index)
			throw new TypeORMError(`Supplied index ${indexOrName} was not found in table ${table.name}`);
		// old index may be passed without name. In this case we generate index name manually.
		if (!index.name) index.name = this.generateIndexName(table, index);

		const up = this.dropIndexSql(table, index);
		const down = this.createIndexSql(table, index);
		await this.executeQueries(up, down);
		table.removeIndex(index);
	}

	/**
	 * Drops an index from a view.
	 */
	async dropViewIndex(viewOrName: View | string, indexOrName: TableIndex | string): Promise<void> {
		const view = InstanceChecker.isView(viewOrName)
			? viewOrName
			: await this.getCachedView(viewOrName);
		const index = InstanceChecker.isTableIndex(indexOrName)
			? indexOrName
			: view.indices.find((i) => i.name === indexOrName);
		if (!index)
			throw new TypeORMError(`Supplied index ${indexOrName} was not found in view ${view.name}`);
		// old index may be passed without name. In this case we generate index name manually.
		if (!index.name) index.name = this.generateIndexName(view, index);

		const up = this.dropIndexSql(view, index);
		const down = this.createViewIndexSql(view, index);
		await this.executeQueries(up, down);
		view.removeIndex(index);
	}

	/**
	 * Drops an indices from the table.
	 */
	async dropIndices(tableOrName: Table | string, indices: TableIndex[]): Promise<void> {
		for (const index of indices) {
			await this.dropIndex(tableOrName, index);
		}
	}

	/**
	 * Clears all table contents.
	 * Note: this operation uses SQL's TRUNCATE query which cannot be reverted in transactions.
	 */
	async clearTable(tableName: string): Promise<void> {
		await this.query(`TRUNCATE TABLE ${this.escapePath(tableName)}`);
	}

	/**
	 * Removes all tables from the currently connected database.
	 */
	async clearDatabase(): Promise<void> {
		const schemas: string[] = [];
		this.connection.entityMetadatas
			.filter((metadata) => metadata.schema)
			.forEach((metadata) => {
				const isSchemaExist = !!schemas.find((schema) => schema === metadata.schema);
				if (!isSchemaExist) schemas.push(metadata.schema!);
			});
		schemas.push(this.driver.options.schema || 'current_schema()');
		const schemaNamesString = schemas
			.map((name) => {
				return name === 'current_schema()' ? name : "'" + name + "'";
			})
			.join(', ');

		const isAnotherTransactionActive = this.isTransactionActive;
		if (!isAnotherTransactionActive) await this.startTransaction();
		try {
			const version = await this.getVersion();
			// drop views
			const selectViewDropsQuery =
				`SELECT 'DROP VIEW IF EXISTS "' || schemaname || '"."' || viewname || '" CASCADE;' as "query" ` +
				`FROM "pg_views" WHERE "schemaname" IN (${schemaNamesString}) AND "viewname" NOT IN ('geography_columns', 'geometry_columns', 'raster_columns', 'raster_overviews')`;
			const dropViewQueries: ObjectLiteral[] = await this.query(selectViewDropsQuery);
			await Promise.all(dropViewQueries.map((q) => this.query(q['query'])));

			// drop materialized views
			// Note: materialized views introduced in Postgres 9.3
			if (VersionUtils.isGreaterOrEqual(version, '9.3')) {
				const selectMatViewDropsQuery =
					`SELECT 'DROP MATERIALIZED VIEW IF EXISTS "' || schemaname || '"."' || matviewname || '" CASCADE;' as "query" ` +
					`FROM "pg_matviews" WHERE "schemaname" IN (${schemaNamesString})`;
				const dropMatViewQueries: ObjectLiteral[] = await this.query(selectMatViewDropsQuery);
				await Promise.all(dropMatViewQueries.map((q) => this.query(q['query'])));
			}

			// ignore spatial_ref_sys; it's a special table supporting PostGIS
			// TODO generalize this as this.driver.ignoreTables

			// drop tables
			const selectTableDropsQuery = `SELECT 'DROP TABLE IF EXISTS "' || schemaname || '"."' || tablename || '" CASCADE;' as "query" FROM "pg_tables" WHERE "schemaname" IN (${schemaNamesString}) AND "tablename" NOT IN ('spatial_ref_sys')`;
			const dropTableQueries: ObjectLiteral[] = await this.query(selectTableDropsQuery);
			await Promise.all(dropTableQueries.map((q) => this.query(q['query'])));

			// drop enum types
			await this.dropEnumTypes(schemaNamesString);

			if (!isAnotherTransactionActive) {
				await this.commitTransaction();
			}
		} catch (error) {
			try {
				// we throw original error even if rollback thrown an error
				if (!isAnotherTransactionActive) {
					await this.rollbackTransaction();
				}
			} catch (rollbackError) {}
			throw error;
		}
	}

	// -------------------------------------------------------------------------
	// Protected Methods
	// -------------------------------------------------------------------------

	protected async loadViews(viewNames?: string[]): Promise<View[]> {
		const hasTable = await this.hasTable(this.getTypeormMetadataTableName());

		if (!hasTable) return [];

		if (!viewNames) {
			viewNames = [];
		}

		const currentDatabase = await this.getCurrentDatabase();
		const currentSchema = await this.getCurrentSchema();
		const viewsCondition =
			viewNames.length === 0
				? '1=1'
				: viewNames
						.map((tableName) => this.driver.parseTableName(tableName))
						.map(({ schema, tableName }) => {
							if (!schema) {
								schema = this.driver.options.schema || currentSchema;
							}

							return `("t"."schema" = '${schema}' AND "t"."name" = '${tableName}')`;
						})
						.join(' OR ');

		const constraintsCondition =
			viewNames.length === 0
				? '1=1'
				: viewNames
						.map((tableName) => this.driver.parseTableName(tableName))
						.map(({ schema, tableName }) => {
							if (!schema) {
								schema = this.driver.options.schema || currentSchema;
							}

							return `("ns"."nspname" = '${schema}' AND "t"."relname" = '${tableName}')`;
						})
						.join(' OR ');

		const indicesSql =
			`SELECT "ns"."nspname" AS "table_schema", "t"."relname" AS "table_name", "i"."relname" AS "constraint_name", "a"."attname" AS "column_name", ` +
			`CASE "ix"."indisunique" WHEN 't' THEN 'TRUE' ELSE'FALSE' END AS "is_unique", pg_get_expr("ix"."indpred", "ix"."indrelid") AS "condition", ` +
			`"types"."typname" AS "type_name" ` +
			`FROM "pg_class" "t" ` +
			`INNER JOIN "pg_index" "ix" ON "ix"."indrelid" = "t"."oid" ` +
			`INNER JOIN "pg_attribute" "a" ON "a"."attrelid" = "t"."oid"  AND "a"."attnum" = ANY ("ix"."indkey") ` +
			`INNER JOIN "pg_namespace" "ns" ON "ns"."oid" = "t"."relnamespace" ` +
			`INNER JOIN "pg_class" "i" ON "i"."oid" = "ix"."indexrelid" ` +
			`INNER JOIN "pg_type" "types" ON "types"."oid" = "a"."atttypid" ` +
			`LEFT JOIN "pg_constraint" "cnst" ON "cnst"."conname" = "i"."relname" ` +
			`WHERE "t"."relkind" IN ('m') AND "cnst"."contype" IS NULL AND (${constraintsCondition})`;

		const query =
			`SELECT "t".* FROM ${this.escapePath(this.getTypeormMetadataTableName())} "t" ` +
			`INNER JOIN "pg_catalog"."pg_class" "c" ON "c"."relname" = "t"."name" ` +
			`INNER JOIN "pg_namespace" "n" ON "n"."oid" = "c"."relnamespace" AND "n"."nspname" = "t"."schema" ` +
			`WHERE "t"."type" IN ('${MetadataTableType.VIEW}', '${
				MetadataTableType.MATERIALIZED_VIEW
			}') ${viewsCondition ? `AND (${viewsCondition})` : ''}`;

		const dbViews = await this.query(query);
		const dbIndices: ObjectLiteral[] = await this.query(indicesSql);
		return dbViews.map((dbView: any) => {
			// find index constraints of table, group them by constraint name and build TableIndex.
			const tableIndexConstraints = OrmUtils.uniq(
				dbIndices.filter((dbIndex) => {
					return (
						dbIndex['table_name'] === dbView['name'] && dbIndex['table_schema'] === dbView['schema']
					);
				}),
				(dbIndex) => dbIndex['constraint_name'],
			);
			const view = new View();
			const schema =
				dbView['schema'] === currentSchema && !this.driver.options.schema
					? undefined
					: dbView['schema'];
			view.database = currentDatabase;
			view.schema = dbView['schema'];
			view.name = this.driver.buildTableName(dbView['name'], schema);
			view.expression = dbView['value'];
			view.materialized = dbView['type'] === MetadataTableType.MATERIALIZED_VIEW;
			view.indices = tableIndexConstraints.map((constraint) => {
				const indices = dbIndices.filter((index) => {
					return (
						index['table_schema'] === constraint['table_schema'] &&
						index['table_name'] === constraint['table_name'] &&
						index['constraint_name'] === constraint['constraint_name']
					);
				});
				return new TableIndex(<TableIndexOptions>{
					view: view,
					name: constraint['constraint_name'],
					columnNames: indices.map((i) => i['column_name']),
					isUnique: constraint['is_unique'] === 'TRUE',
					where: constraint['condition'],
					isFulltext: false,
				});
			});
			return view;
		});
	}

	/**
	 * Loads all tables (with given names) from the database and creates a Table from them.
	 */
	protected async loadTables(tableNames?: string[]): Promise<Table[]> {
		// if no tables given then no need to proceed
		if (tableNames && tableNames.length === 0) {
			return [];
		}

		const currentSchema = await this.getCurrentSchema();
		const currentDatabase = await this.getCurrentDatabase();

		const dbTables: {
			table_schema: string;
			table_name: string;
			table_comment: string;
		}[] = [];

		if (!tableNames) {
			const tablesSql = `SELECT "table_schema", "table_name", obj_description(('"' || "table_schema" || '"."' || "table_name" || '"')::regclass, 'pg_class') AS table_comment FROM "information_schema"."tables"`;
			dbTables.push(...(await this.query(tablesSql)));
		} else {
			const tablesCondition = tableNames
				.map((tableName) => this.driver.parseTableName(tableName))
				.map(({ schema, tableName }) => {
					return `("table_schema" = '${
						schema || currentSchema
					}' AND "table_name" = '${tableName}')`;
				})
				.join(' OR ');

			const tablesSql =
				`SELECT "table_schema", "table_name", obj_description(('"' || "table_schema" || '"."' || "table_name" || '"')::regclass, 'pg_class') AS table_comment FROM "information_schema"."tables" WHERE ` +
				tablesCondition;
			dbTables.push(...(await this.query(tablesSql)));
		}

		// if tables were not found in the db, no need to proceed
		if (dbTables.length === 0) {
			return [];
		}

		/**
		 * Uses standard SQL information_schema.columns table and postgres-specific
		 * pg_catalog.pg_attribute table to get column information.
		 * @see https://stackoverflow.com/a/19541865
		 */
		const columnsCondition = dbTables
			.map(({ table_schema, table_name }) => {
				return `("table_schema" = '${table_schema}' AND "table_name" = '${table_name}')`;
			})
			.join(' OR ');
		const columnsSql =
			`SELECT columns.*, pg_catalog.col_description(('"' || table_catalog || '"."' || table_schema || '"."' || table_name || '"')::regclass::oid, ordinal_position) AS description, ` +
			`('"' || "udt_schema" || '"."' || "udt_name" || '"')::"regtype" AS "regtype", pg_catalog.format_type("col_attr"."atttypid", "col_attr"."atttypmod") AS "format_type" ` +
			`FROM "information_schema"."columns" ` +
			`LEFT JOIN "pg_catalog"."pg_attribute" AS "col_attr" ON "col_attr"."attname" = "columns"."column_name" ` +
			`AND "col_attr"."attrelid" = ( ` +
			`SELECT "cls"."oid" FROM "pg_catalog"."pg_class" AS "cls" ` +
			`LEFT JOIN "pg_catalog"."pg_namespace" AS "ns" ON "ns"."oid" = "cls"."relnamespace" ` +
			`WHERE "cls"."relname" = "columns"."table_name" ` +
			`AND "ns"."nspname" = "columns"."table_schema" ` +
			`) ` +
			`WHERE ` +
			columnsCondition;

		const constraintsCondition = dbTables
			.map(({ table_schema, table_name }) => {
				return `("ns"."nspname" = '${table_schema}' AND "t"."relname" = '${table_name}')`;
			})
			.join(' OR ');

		const constraintsSql =
			`SELECT "ns"."nspname" AS "table_schema", "t"."relname" AS "table_name", "cnst"."conname" AS "constraint_name", ` +
			`pg_get_constraintdef("cnst"."oid") AS "expression", ` +
			`CASE "cnst"."contype" WHEN 'p' THEN 'PRIMARY' WHEN 'u' THEN 'UNIQUE' WHEN 'c' THEN 'CHECK' WHEN 'x' THEN 'EXCLUDE' END AS "constraint_type", "a"."attname" AS "column_name" ` +
			`FROM "pg_constraint" "cnst" ` +
			`INNER JOIN "pg_class" "t" ON "t"."oid" = "cnst"."conrelid" ` +
			`INNER JOIN "pg_namespace" "ns" ON "ns"."oid" = "cnst"."connamespace" ` +
			`LEFT JOIN "pg_attribute" "a" ON "a"."attrelid" = "cnst"."conrelid" AND "a"."attnum" = ANY ("cnst"."conkey") ` +
			`WHERE "t"."relkind" IN ('r', 'p') AND (${constraintsCondition})`;

		const indicesSql =
			`SELECT "ns"."nspname" AS "table_schema", "t"."relname" AS "table_name", "i"."relname" AS "constraint_name", "a"."attname" AS "column_name", ` +
			`CASE "ix"."indisunique" WHEN 't' THEN 'TRUE' ELSE'FALSE' END AS "is_unique", pg_get_expr("ix"."indpred", "ix"."indrelid") AS "condition", ` +
			`"types"."typname" AS "type_name", "am"."amname" AS "index_type" ` +
			`FROM "pg_class" "t" ` +
			`INNER JOIN "pg_index" "ix" ON "ix"."indrelid" = "t"."oid" ` +
			`INNER JOIN "pg_attribute" "a" ON "a"."attrelid" = "t"."oid"  AND "a"."attnum" = ANY ("ix"."indkey") ` +
			`INNER JOIN "pg_namespace" "ns" ON "ns"."oid" = "t"."relnamespace" ` +
			`INNER JOIN "pg_class" "i" ON "i"."oid" = "ix"."indexrelid" ` +
			`INNER JOIN "pg_type" "types" ON "types"."oid" = "a"."atttypid" ` +
			`INNER JOIN "pg_am" "am" ON "i"."relam" = "am"."oid" ` +
			`LEFT JOIN "pg_constraint" "cnst" ON "cnst"."conname" = "i"."relname" ` +
			`WHERE "t"."relkind" IN ('r', 'p') AND "cnst"."contype" IS NULL AND (${constraintsCondition})`;

		const foreignKeysCondition = dbTables
			.map(({ table_schema, table_name }) => {
				return `("ns"."nspname" = '${table_schema}' AND "cl"."relname" = '${table_name}')`;
			})
			.join(' OR ');

		const hasRelispartitionColumn = await this.hasSupportForPartitionedTables();
		const isPartitionCondition = hasRelispartitionColumn ? ` AND "cl"."relispartition" = 'f'` : '';

		const foreignKeysSql =
			`SELECT "con"."conname" AS "constraint_name", "con"."nspname" AS "table_schema", "con"."relname" AS "table_name", "att2"."attname" AS "column_name", ` +
			`"ns"."nspname" AS "referenced_table_schema", "cl"."relname" AS "referenced_table_name", "att"."attname" AS "referenced_column_name", "con"."confdeltype" AS "on_delete", ` +
			`"con"."confupdtype" AS "on_update", "con"."condeferrable" AS "deferrable", "con"."condeferred" AS "deferred" ` +
			`FROM ( ` +
			`SELECT UNNEST ("con1"."conkey") AS "parent", UNNEST ("con1"."confkey") AS "child", "con1"."confrelid", "con1"."conrelid", "con1"."conname", "con1"."contype", "ns"."nspname", ` +
			`"cl"."relname", "con1"."condeferrable", ` +
			`CASE WHEN "con1"."condeferred" THEN 'INITIALLY DEFERRED' ELSE 'INITIALLY IMMEDIATE' END as condeferred, ` +
			`CASE "con1"."confdeltype" WHEN 'a' THEN 'NO ACTION' WHEN 'r' THEN 'RESTRICT' WHEN 'c' THEN 'CASCADE' WHEN 'n' THEN 'SET NULL' WHEN 'd' THEN 'SET DEFAULT' END as "confdeltype", ` +
			`CASE "con1"."confupdtype" WHEN 'a' THEN 'NO ACTION' WHEN 'r' THEN 'RESTRICT' WHEN 'c' THEN 'CASCADE' WHEN 'n' THEN 'SET NULL' WHEN 'd' THEN 'SET DEFAULT' END as "confupdtype" ` +
			`FROM "pg_class" "cl" ` +
			`INNER JOIN "pg_namespace" "ns" ON "cl"."relnamespace" = "ns"."oid" ` +
			`INNER JOIN "pg_constraint" "con1" ON "con1"."conrelid" = "cl"."oid" ` +
			`WHERE "con1"."contype" = 'f' AND (${foreignKeysCondition}) ` +
			`) "con" ` +
			`INNER JOIN "pg_attribute" "att" ON "att"."attrelid" = "con"."confrelid" AND "att"."attnum" = "con"."child" ` +
			`INNER JOIN "pg_class" "cl" ON "cl"."oid" = "con"."confrelid" ${isPartitionCondition}` +
			`INNER JOIN "pg_namespace" "ns" ON "cl"."relnamespace" = "ns"."oid" ` +
			`INNER JOIN "pg_attribute" "att2" ON "att2"."attrelid" = "con"."conrelid" AND "att2"."attnum" = "con"."parent"`;

		const [dbColumns, dbConstraints, dbIndices, dbForeignKeys]: ObjectLiteral[][] =
			await Promise.all([
				this.query(columnsSql),
				this.query(constraintsSql),
				this.query(indicesSql),
				this.query(foreignKeysSql),
			]);

		// create tables for loaded tables
		return Promise.all(
			dbTables.map(async (dbTable) => {
				const table = new Table();

				const getSchemaFromKey = (dbObject: any, key: string) => {
					return dbObject[key] === currentSchema &&
						(!this.driver.options.schema || this.driver.options.schema === currentSchema)
						? undefined
						: dbObject[key];
				};
				// We do not need to join schema name, when database is by default.
				const schema = getSchemaFromKey(dbTable, 'table_schema');
				table.database = currentDatabase;
				table.schema = dbTable['table_schema'];
				table.comment = dbTable['table_comment'];
				table.name = this.driver.buildTableName(dbTable['table_name'], schema);

				// create columns from the loaded columns
				table.columns = await Promise.all(
					dbColumns
						.filter(
							(dbColumn) =>
								dbColumn['table_name'] === dbTable['table_name'] &&
								dbColumn['table_schema'] === dbTable['table_schema'],
						)
						.map(async (dbColumn) => {
							const columnConstraints = dbConstraints.filter((dbConstraint) => {
								return (
									dbConstraint['table_name'] === dbColumn['table_name'] &&
									dbConstraint['table_schema'] === dbColumn['table_schema'] &&
									dbConstraint['column_name'] === dbColumn['column_name']
								);
							});

							const tableColumn = new TableColumn();
							tableColumn.name = dbColumn['column_name'];
							tableColumn.type = dbColumn['regtype'].toLowerCase();

							if (
								tableColumn.type === 'numeric' ||
								tableColumn.type === 'numeric[]' ||
								tableColumn.type === 'decimal' ||
								tableColumn.type === 'float'
							) {
								let numericPrecision = dbColumn['numeric_precision'];
								let numericScale = dbColumn['numeric_scale'];
								if (dbColumn['data_type'] === 'ARRAY') {
									const numericSize = dbColumn['format_type'].match(
										/^numeric\(([0-9]+),([0-9]+)\)\[\]$/,
									);
									if (numericSize) {
										numericPrecision = +numericSize[1];
										numericScale = +numericSize[2];
									}
								}
								// If one of these properties was set, and another was not, Postgres sets '0' in to unspecified property
								// we set 'undefined' in to unspecified property to avoid changing column on sync
								if (
									numericPrecision !== null &&
									!this.isDefaultColumnPrecision(table, tableColumn, numericPrecision)
								) {
									tableColumn.precision = numericPrecision;
								} else if (
									numericScale !== null &&
									!this.isDefaultColumnScale(table, tableColumn, numericScale)
								) {
									tableColumn.precision = undefined;
								}
								if (
									numericScale !== null &&
									!this.isDefaultColumnScale(table, tableColumn, numericScale)
								) {
									tableColumn.scale = numericScale;
								} else if (
									numericPrecision !== null &&
									!this.isDefaultColumnPrecision(table, tableColumn, numericPrecision)
								) {
									tableColumn.scale = undefined;
								}
							}

							if (
								tableColumn.type === 'interval' ||
								tableColumn.type === 'time without time zone' ||
								tableColumn.type === 'time with time zone' ||
								tableColumn.type === 'timestamp without time zone' ||
								tableColumn.type === 'timestamp with time zone'
							) {
								tableColumn.precision = !this.isDefaultColumnPrecision(
									table,
									tableColumn,
									dbColumn['datetime_precision'],
								)
									? dbColumn['datetime_precision']
									: undefined;
							}

							// check if column has user-defined data type.
							// NOTE: if ENUM type defined with "array:true" it comes with ARRAY type instead of USER-DEFINED
							if (dbColumn['data_type'] === 'USER-DEFINED' || dbColumn['data_type'] === 'ARRAY') {
								const { name } = await this.getUserDefinedTypeName(table, tableColumn);

								// check if `enumName` is specified by user
								const builtEnumName = this.buildEnumName(table, tableColumn, false, true);
								const enumName = builtEnumName !== name ? name : undefined;

								// check if type is ENUM
								const sql =
									`SELECT "e"."enumlabel" AS "value" FROM "pg_enum" "e" ` +
									`INNER JOIN "pg_type" "t" ON "t"."oid" = "e"."enumtypid" ` +
									`INNER JOIN "pg_namespace" "n" ON "n"."oid" = "t"."typnamespace" ` +
									`WHERE "n"."nspname" = '${dbTable['table_schema']}' AND "t"."typname" = '${
										enumName || name
									}'`;
								const results: ObjectLiteral[] = await this.query(sql);

								if (results.length) {
									tableColumn.type = 'enum';
									tableColumn.enum = results.map((result) => result['value']);
									tableColumn.enumName = enumName;
								}

								if (dbColumn['data_type'] === 'ARRAY') {
									tableColumn.isArray = true;
									const type = tableColumn.type.replace('[]', '');
									tableColumn.type = this.connection.driver.normalizeType({
										type: type,
									});
								}
							}

							if (tableColumn.type === 'geometry' || tableColumn.type === 'geography') {
								const sql =
									`SELECT * FROM (` +
									`SELECT "f_table_schema" "table_schema", "f_table_name" "table_name", ` +
									`"f_${tableColumn.type}_column" "column_name", "srid", "type" ` +
									`FROM "${tableColumn.type}_columns"` +
									`) AS _ ` +
									`WHERE "column_name" = '${dbColumn['column_name']}' AND ` +
									`"table_schema" = '${dbColumn['table_schema']}' AND ` +
									`"table_name" = '${dbColumn['table_name']}'`;

								const results: ObjectLiteral[] = await this.query(sql);

								if (results.length > 0) {
									tableColumn.spatialFeatureType = results[0].type;
									tableColumn.srid = results[0].srid;
								}
							}

							// check only columns that have length property
							if (
								this.driver.withLengthColumnTypes.indexOf(tableColumn.type as ColumnType) !== -1
							) {
								let length;
								if (tableColumn.isArray) {
									const match = /\((\d+)\)/.exec(dbColumn['format_type']);
									length = match ? match[1] : undefined;
								} else if (dbColumn['character_maximum_length']) {
									length = dbColumn['character_maximum_length'].toString();
								}
								if (length) {
									tableColumn.length = !this.isDefaultColumnLength(table, tableColumn, length)
										? length
										: '';
								}
							}
							tableColumn.isNullable = dbColumn['is_nullable'] === 'YES';

							const primaryConstraint = columnConstraints.find(
								(constraint) => constraint['constraint_type'] === 'PRIMARY',
							);
							if (primaryConstraint) {
								tableColumn.isPrimary = true;
								// find another columns involved in primary key constraint
								const anotherPrimaryConstraints = dbConstraints.filter(
									(constraint) =>
										constraint['table_name'] === dbColumn['table_name'] &&
										constraint['table_schema'] === dbColumn['table_schema'] &&
										constraint['column_name'] !== dbColumn['column_name'] &&
										constraint['constraint_type'] === 'PRIMARY',
								);

								// collect all column names
								const columnNames = anotherPrimaryConstraints.map(
									(constraint) => constraint['column_name'],
								);
								columnNames.push(dbColumn['column_name']);

								// build default primary key constraint name
								const pkName = this.connection.namingStrategy.primaryKeyName(table, columnNames);

								// if primary key has user-defined constraint name, write it in table column
								if (primaryConstraint['constraint_name'] !== pkName) {
									tableColumn.primaryKeyConstraintName = primaryConstraint['constraint_name'];
								}
							}

							const uniqueConstraints = columnConstraints.filter(
								(constraint) => constraint['constraint_type'] === 'UNIQUE',
							);
							const isConstraintComposite = uniqueConstraints.every((uniqueConstraint) => {
								return dbConstraints.some(
									(dbConstraint) =>
										dbConstraint['constraint_type'] === 'UNIQUE' &&
										dbConstraint['constraint_name'] === uniqueConstraint['constraint_name'] &&
										dbConstraint['column_name'] !== dbColumn['column_name'],
								);
							});
							tableColumn.isUnique = uniqueConstraints.length > 0 && !isConstraintComposite;

							if (dbColumn.is_identity === 'YES') {
								// Postgres 10+ Identity column
								tableColumn.isGenerated = true;
								tableColumn.generationStrategy = 'identity';
								tableColumn.generatedIdentity = dbColumn.identity_generation;
							} else if (
								dbColumn['column_default'] !== null &&
								dbColumn['column_default'] !== undefined
							) {
								const serialDefaultName = `nextval('${this.buildSequenceName(
									table,
									dbColumn['column_name'],
								)}'::regclass)`;
								const serialDefaultPath = `nextval('${this.buildSequencePath(
									table,
									dbColumn['column_name'],
								)}'::regclass)`;

								const defaultWithoutQuotes = dbColumn['column_default'].replace(/"/g, '');

								if (
									defaultWithoutQuotes === serialDefaultName ||
									defaultWithoutQuotes === serialDefaultPath
								) {
									tableColumn.isGenerated = true;
									tableColumn.generationStrategy = 'increment';
								} else if (
									dbColumn['column_default'] === 'gen_random_uuid()' ||
									/^uuid_generate_v\d\(\)/.test(dbColumn['column_default'])
								) {
									if (tableColumn.type === 'uuid') {
										tableColumn.isGenerated = true;
										tableColumn.generationStrategy = 'uuid';
									} else {
										tableColumn.default = dbColumn['column_default'];
									}
								} else if (
									dbColumn['column_default'] === 'now()' ||
									dbColumn['column_default'].indexOf("'now'::text") !== -1
								) {
									tableColumn.default = dbColumn['column_default'];
								} else {
									tableColumn.default = dbColumn['column_default'].replace(/::[\w\s.[\]\-"]+/g, '');
									tableColumn.default = tableColumn.default.replace(/^(-?\d+)$/, "'$1'");
								}
							}

							if (dbColumn['is_generated'] === 'ALWAYS' && dbColumn['generation_expression']) {
								// In postgres there is no VIRTUAL generated column type
								tableColumn.generatedType = 'STORED';
								// We cannot relay on information_schema.columns.generation_expression, because it is formatted different.
								const asExpressionQuery = this.selectTypeormMetadataSql({
									database: currentDatabase,
									schema: dbTable['table_schema'],
									table: dbTable['table_name'],
									type: MetadataTableType.GENERATED_COLUMN,
									name: tableColumn.name,
								});

								const results = await this.query(
									asExpressionQuery.query,
									asExpressionQuery.parameters,
								);
								if (results[0] && results[0].value) {
									tableColumn.asExpression = results[0].value;
								} else {
									tableColumn.asExpression = '';
								}
							}

							tableColumn.comment = dbColumn['description'] ? dbColumn['description'] : undefined;
							if (dbColumn['character_set_name'])
								tableColumn.charset = dbColumn['character_set_name'];
							if (dbColumn['collation_name']) tableColumn.collation = dbColumn['collation_name'];
							return tableColumn;
						}),
				);

				// find unique constraints of table, group them by constraint name and build TableUnique.
				const tableUniqueConstraints = OrmUtils.uniq(
					dbConstraints.filter((dbConstraint) => {
						return (
							dbConstraint['table_name'] === dbTable['table_name'] &&
							dbConstraint['table_schema'] === dbTable['table_schema'] &&
							dbConstraint['constraint_type'] === 'UNIQUE'
						);
					}),
					(dbConstraint) => dbConstraint['constraint_name'],
				);

				table.uniques = tableUniqueConstraints.map((constraint) => {
					const uniques = dbConstraints.filter(
						(dbC) => dbC['constraint_name'] === constraint['constraint_name'],
					);
					return new TableUnique({
						name: constraint['constraint_name'],
						columnNames: uniques.map((u) => u['column_name']),
						deferrable: constraint['deferrable'] ? constraint['deferred'] : undefined,
					});
				});

				// find check constraints of table, group them by constraint name and build TableCheck.
				const tableCheckConstraints = OrmUtils.uniq(
					dbConstraints.filter((dbConstraint) => {
						return (
							dbConstraint['table_name'] === dbTable['table_name'] &&
							dbConstraint['table_schema'] === dbTable['table_schema'] &&
							dbConstraint['constraint_type'] === 'CHECK'
						);
					}),
					(dbConstraint) => dbConstraint['constraint_name'],
				);

				table.checks = tableCheckConstraints.map((constraint) => {
					const checks = dbConstraints.filter(
						(dbC) => dbC['constraint_name'] === constraint['constraint_name'],
					);
					return new TableCheck({
						name: constraint['constraint_name'],
						columnNames: checks.map((c) => c['column_name']),
						expression: constraint['expression'].replace(/^\s*CHECK\s*\((.*)\)\s*$/i, '$1'),
					});
				});

				// find exclusion constraints of table, group them by constraint name and build TableExclusion.
				const tableExclusionConstraints = OrmUtils.uniq(
					dbConstraints.filter((dbConstraint) => {
						return (
							dbConstraint['table_name'] === dbTable['table_name'] &&
							dbConstraint['table_schema'] === dbTable['table_schema'] &&
							dbConstraint['constraint_type'] === 'EXCLUDE'
						);
					}),
					(dbConstraint) => dbConstraint['constraint_name'],
				);

				table.exclusions = tableExclusionConstraints.map((constraint) => {
					return new TableExclusion({
						name: constraint['constraint_name'],
						expression: constraint['expression'].substring(8), // trim EXCLUDE from start of expression
					});
				});

				// find foreign key constraints of table, group them by constraint name and build TableForeignKey.
				const tableForeignKeyConstraints = OrmUtils.uniq(
					dbForeignKeys.filter((dbForeignKey) => {
						return (
							dbForeignKey['table_name'] === dbTable['table_name'] &&
							dbForeignKey['table_schema'] === dbTable['table_schema']
						);
					}),
					(dbForeignKey) => dbForeignKey['constraint_name'],
				);

				table.foreignKeys = tableForeignKeyConstraints.map((dbForeignKey) => {
					const foreignKeys = dbForeignKeys.filter(
						(dbFk) => dbFk['constraint_name'] === dbForeignKey['constraint_name'],
					);

					// if referenced table located in currently used schema, we don't need to concat schema name to table name.
					const schema = getSchemaFromKey(dbForeignKey, 'referenced_table_schema');
					const referencedTableName = this.driver.buildTableName(
						dbForeignKey['referenced_table_name'],
						schema,
					);

					return new TableForeignKey({
						name: dbForeignKey['constraint_name'],
						columnNames: foreignKeys.map((dbFk) => dbFk['column_name']),
						referencedSchema: dbForeignKey['referenced_table_schema'],
						referencedTableName: referencedTableName,
						referencedColumnNames: foreignKeys.map((dbFk) => dbFk['referenced_column_name']),
						onDelete: dbForeignKey['on_delete'],
						onUpdate: dbForeignKey['on_update'],
						deferrable: dbForeignKey['deferrable'] ? dbForeignKey['deferred'] : undefined,
					});
				});

				// find index constraints of table, group them by constraint name and build TableIndex.
				const tableIndexConstraints = OrmUtils.uniq(
					dbIndices.filter((dbIndex) => {
						return (
							dbIndex['table_name'] === dbTable['table_name'] &&
							dbIndex['table_schema'] === dbTable['table_schema']
						);
					}),
					(dbIndex) => dbIndex['constraint_name'],
				);

				table.indices = tableIndexConstraints.map((constraint) => {
					const indices = dbIndices.filter((index) => {
						return (
							index['table_schema'] === constraint['table_schema'] &&
							index['table_name'] === constraint['table_name'] &&
							index['constraint_name'] === constraint['constraint_name']
						);
					});
					return new TableIndex(<TableIndexOptions>{
						table: table,
						name: constraint['constraint_name'],
						columnNames: indices.map((i) => i['column_name']),
						isUnique: constraint['is_unique'] === 'TRUE',
						where: constraint['condition'],
						isSpatial: constraint['index_type'] === 'gist',
						isFulltext: false,
					});
				});

				return table;
			}),
		);
	}

	/**
	 * Builds create table sql.
	 */
	protected createTableSql(table: Table, createForeignKeys?: boolean): Query {
		const columnDefinitions = table.columns
			.map((column) => this.buildCreateColumnSql(table, column))
			.join(', ');
		let sql = `CREATE TABLE ${this.escapePath(table)} (${columnDefinitions}`;

		table.columns
			.filter((column) => column.isUnique)
			.forEach((column) => {
				const isUniqueExist = table.uniques.some(
					(unique) => unique.columnNames.length === 1 && unique.columnNames[0] === column.name,
				);
				if (!isUniqueExist)
					table.uniques.push(
						new TableUnique({
							name: this.connection.namingStrategy.uniqueConstraintName(table, [column.name]),
							columnNames: [column.name],
						}),
					);
			});

		if (table.uniques.length > 0) {
			const uniquesSql = table.uniques
				.map((unique) => {
					const uniqueName = unique.name
						? unique.name
						: this.connection.namingStrategy.uniqueConstraintName(table, unique.columnNames);
					const columnNames = unique.columnNames.map((columnName) => `"${columnName}"`).join(', ');
					let constraint = `CONSTRAINT "${uniqueName}" UNIQUE (${columnNames})`;
					if (unique.deferrable) constraint += ` DEFERRABLE ${unique.deferrable}`;
					return constraint;
				})
				.join(', ');

			sql += `, ${uniquesSql}`;
		}

		if (table.checks.length > 0) {
			const checksSql = table.checks
				.map((check) => {
					const checkName = check.name
						? check.name
						: this.connection.namingStrategy.checkConstraintName(table, check.expression!);
					return `CONSTRAINT "${checkName}" CHECK (${check.expression})`;
				})
				.join(', ');

			sql += `, ${checksSql}`;
		}

		if (table.exclusions.length > 0) {
			const exclusionsSql = table.exclusions
				.map((exclusion) => {
					const exclusionName = exclusion.name
						? exclusion.name
						: this.connection.namingStrategy.exclusionConstraintName(table, exclusion.expression!);
					return `CONSTRAINT "${exclusionName}" EXCLUDE ${exclusion.expression}`;
				})
				.join(', ');

			sql += `, ${exclusionsSql}`;
		}

		if (table.foreignKeys.length > 0 && createForeignKeys) {
			const foreignKeysSql = table.foreignKeys
				.map((fk) => {
					const columnNames = fk.columnNames.map((columnName) => `"${columnName}"`).join(', ');
					if (!fk.name)
						fk.name = this.connection.namingStrategy.foreignKeyName(
							table,
							fk.columnNames,
							this.getTablePath(fk),
							fk.referencedColumnNames,
						);

					const referencedColumnNames = fk.referencedColumnNames
						.map((columnName) => `"${columnName}"`)
						.join(', ');

					let constraint = `CONSTRAINT "${
						fk.name
					}" FOREIGN KEY (${columnNames}) REFERENCES ${this.escapePath(
						this.getTablePath(fk),
					)} (${referencedColumnNames})`;
					if (fk.onDelete) constraint += ` ON DELETE ${fk.onDelete}`;
					if (fk.onUpdate) constraint += ` ON UPDATE ${fk.onUpdate}`;
					if (fk.deferrable) constraint += ` DEFERRABLE ${fk.deferrable}`;

					return constraint;
				})
				.join(', ');

			sql += `, ${foreignKeysSql}`;
		}

		const primaryColumns = table.columns.filter((column) => column.isPrimary);
		if (primaryColumns.length > 0) {
			const primaryKeyName = primaryColumns[0].primaryKeyConstraintName
				? primaryColumns[0].primaryKeyConstraintName
				: this.connection.namingStrategy.primaryKeyName(
						table,
						primaryColumns.map((column) => column.name),
					);

			const columnNames = primaryColumns.map((column) => `"${column.name}"`).join(', ');
			sql += `, CONSTRAINT "${primaryKeyName}" PRIMARY KEY (${columnNames})`;
		}

		sql += `)`;

		table.columns
			.filter((it) => it.comment)
			.forEach(
				(it) =>
					(sql += `; COMMENT ON COLUMN ${this.escapePath(table)}."${
						it.name
					}" IS ${this.escapeComment(it.comment)}`),
			);

		return new Query(sql);
	}

	/**
	 * Loads Postgres version.
	 */
	protected async getVersion(): Promise<string> {
		const result = await this.query(`SELECT version()`);
		return result[0]['version'].replace(/^PostgreSQL ([\d.]+) .*$/, '$1');
	}

	/**
	 * Builds drop table sql.
	 */
	protected dropTableSql(tableOrPath: Table | string): Query {
		return new Query(`DROP TABLE ${this.escapePath(tableOrPath)}`);
	}

	protected createViewSql(view: View): Query {
		const materializedClause = view.materialized ? 'MATERIALIZED ' : '';
		const viewName = this.escapePath(view);

		if (typeof view.expression === 'string') {
			return new Query(`CREATE ${materializedClause}VIEW ${viewName} AS ${view.expression}`);
		} else {
			return new Query(
				`CREATE ${materializedClause}VIEW ${viewName} AS ${view
					.expression(this.connection)
					.getQuery()}`,
			);
		}
	}

	protected async insertViewDefinitionSql(view: View): Promise<Query> {
		const currentSchema = await this.getCurrentSchema();

		let { schema, tableName: name } = this.driver.parseTableName(view);

		if (!schema) {
			schema = currentSchema;
		}

		const type = view.materialized ? MetadataTableType.MATERIALIZED_VIEW : MetadataTableType.VIEW;
		const expression =
			typeof view.expression === 'string'
				? view.expression.trim()
				: view.expression(this.connection).getQuery();
		return this.insertTypeormMetadataSql({
			type,
			schema,
			name,
			value: expression,
		});
	}

	/**
	 * Builds drop view sql.
	 */
	protected dropViewSql(view: View): Query {
		const materializedClause = view.materialized ? 'MATERIALIZED ' : '';
		return new Query(`DROP ${materializedClause}VIEW ${this.escapePath(view)}`);
	}

	/**
	 * Builds remove view sql.
	 */
	protected async deleteViewDefinitionSql(view: View): Promise<Query> {
		const currentSchema = await this.getCurrentSchema();

		let { schema, tableName: name } = this.driver.parseTableName(view);

		if (!schema) {
			schema = currentSchema;
		}

		const type = view.materialized ? MetadataTableType.MATERIALIZED_VIEW : MetadataTableType.VIEW;
		return this.deleteTypeormMetadataSql({ type, schema, name });
	}

	/**
	 * Drops ENUM type from given schemas.
	 */
	protected async dropEnumTypes(schemaNames: string): Promise<void> {
		const selectDropsQuery =
			`SELECT 'DROP TYPE IF EXISTS "' || n.nspname || '"."' || t.typname || '" CASCADE;' as "query" FROM "pg_type" "t" ` +
			`INNER JOIN "pg_enum" "e" ON "e"."enumtypid" = "t"."oid" ` +
			`INNER JOIN "pg_namespace" "n" ON "n"."oid" = "t"."typnamespace" ` +
			`WHERE "n"."nspname" IN (${schemaNames}) GROUP BY "n"."nspname", "t"."typname"`;
		const dropQueries: ObjectLiteral[] = await this.query(selectDropsQuery);
		await Promise.all(dropQueries.map((q) => this.query(q['query'])));
	}

	/**
	 * Checks if enum with the given name exist in the database.
	 */
	protected async hasEnumType(table: Table, column: TableColumn): Promise<boolean> {
		let { schema } = this.driver.parseTableName(table);

		if (!schema) {
			schema = await this.getCurrentSchema();
		}

		const enumName = this.buildEnumName(table, column, false, true);
		const sql =
			`SELECT "n"."nspname", "t"."typname" FROM "pg_type" "t" ` +
			`INNER JOIN "pg_namespace" "n" ON "n"."oid" = "t"."typnamespace" ` +
			`WHERE "n"."nspname" = $1 AND "t"."typname" = $2`;
		const result = await this.query(sql, [schema, enumName]);
		return result.length ? true : false;
	}

	/**
	 * Builds create ENUM type sql.
	 */
	protected createEnumTypeSql(table: Table, column: TableColumn, enumName?: string): Query {
		if (!enumName) enumName = this.buildEnumName(table, column);
		const enumValues = column.enum!.map((value) => `'${value.replace("'", "''")}'`).join(', ');
		return new Query(`CREATE TYPE ${enumName} AS ENUM(${enumValues})`);
	}

	/**
	 * Builds create ENUM type sql.
	 */
	protected dropEnumTypeSql(table: Table, column: TableColumn, enumName?: string): Query {
		if (!enumName) enumName = this.buildEnumName(table, column);
		return new Query(`DROP TYPE ${enumName}`);
	}

	/**
	 * Builds create index sql.
	 */
	protected createIndexSql(table: Table, index: TableIndex): Query {
		const columns = index.columnNames.map((columnName) => `"${columnName}"`).join(', ');
		return new Query(
			`CREATE ${index.isUnique ? 'UNIQUE ' : ''}INDEX${
				index.isConcurrent ? ' CONCURRENTLY' : ''
			} "${index.name}" ON ${this.escapePath(table)} ${
				index.isSpatial ? 'USING GiST ' : ''
			}(${columns}) ${index.where ? 'WHERE ' + index.where : ''}`,
		);
	}

	/**
	 * Builds create view index sql.
	 */
	protected createViewIndexSql(view: View, index: TableIndex): Query {
		const columns = index.columnNames.map((columnName) => `"${columnName}"`).join(', ');
		return new Query(
			`CREATE ${index.isUnique ? 'UNIQUE ' : ''}INDEX "${
				index.name
			}" ON ${this.escapePath(view)} (${columns}) ${index.where ? 'WHERE ' + index.where : ''}`,
		);
	}

	/**
	 * Builds drop index sql.
	 */
	protected dropIndexSql(table: Table | View, indexOrName: TableIndex | string): Query {
		const indexName = InstanceChecker.isTableIndex(indexOrName) ? indexOrName.name : indexOrName;
		const concurrent = InstanceChecker.isTableIndex(indexOrName) ? indexOrName.isConcurrent : false;
		const { schema } = this.driver.parseTableName(table);
		return schema
			? new Query(`DROP INDEX ${concurrent ? 'CONCURRENTLY ' : ''}"${schema}"."${indexName}"`)
			: new Query(`DROP INDEX ${concurrent ? 'CONCURRENTLY ' : ''}"${indexName}"`);
	}

	/**
	 * Builds create primary key sql.
	 */
	protected createPrimaryKeySql(
		table: Table,
		columnNames: string[],
		constraintName?: string,
	): Query {
		const primaryKeyName = constraintName
			? constraintName
			: this.connection.namingStrategy.primaryKeyName(table, columnNames);

		const columnNamesString = columnNames.map((columnName) => `"${columnName}"`).join(', ');

		return new Query(
			`ALTER TABLE ${this.escapePath(
				table,
			)} ADD CONSTRAINT "${primaryKeyName}" PRIMARY KEY (${columnNamesString})`,
		);
	}

	/**
	 * Builds drop primary key sql.
	 */
	protected dropPrimaryKeySql(table: Table): Query {
		if (!table.primaryColumns.length) throw new TypeORMError(`Table ${table} has no primary keys.`);

		const columnNames = table.primaryColumns.map((column) => column.name);
		const constraintName = table.primaryColumns[0].primaryKeyConstraintName;
		const primaryKeyName = constraintName
			? constraintName
			: this.connection.namingStrategy.primaryKeyName(table, columnNames);

		return new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${primaryKeyName}"`);
	}

	/**
	 * Builds create unique constraint sql.
	 */
	protected createUniqueConstraintSql(table: Table, uniqueConstraint: TableUnique): Query {
		const columnNames = uniqueConstraint.columnNames.map((column) => `"` + column + `"`).join(', ');
		let sql = `ALTER TABLE ${this.escapePath(table)} ADD CONSTRAINT "${
			uniqueConstraint.name
		}" UNIQUE (${columnNames})`;
		if (uniqueConstraint.deferrable) sql += ` DEFERRABLE ${uniqueConstraint.deferrable}`;
		return new Query(sql);
	}

	/**
	 * Builds drop unique constraint sql.
	 */
	protected dropUniqueConstraintSql(table: Table, uniqueOrName: TableUnique | string): Query {
		const uniqueName = InstanceChecker.isTableUnique(uniqueOrName)
			? uniqueOrName.name
			: uniqueOrName;
		return new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${uniqueName}"`);
	}

	/**
	 * Builds create check constraint sql.
	 */
	protected createCheckConstraintSql(table: Table, checkConstraint: TableCheck): Query {
		return new Query(
			`ALTER TABLE ${this.escapePath(table)} ADD CONSTRAINT "${
				checkConstraint.name
			}" CHECK (${checkConstraint.expression})`,
		);
	}

	/**
	 * Builds drop check constraint sql.
	 */
	protected dropCheckConstraintSql(table: Table, checkOrName: TableCheck | string): Query {
		const checkName = InstanceChecker.isTableCheck(checkOrName) ? checkOrName.name : checkOrName;
		return new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${checkName}"`);
	}

	/**
	 * Builds create exclusion constraint sql.
	 */
	protected createExclusionConstraintSql(table: Table, exclusionConstraint: TableExclusion): Query {
		return new Query(
			`ALTER TABLE ${this.escapePath(table)} ADD CONSTRAINT "${
				exclusionConstraint.name
			}" EXCLUDE ${exclusionConstraint.expression}`,
		);
	}

	/**
	 * Builds drop exclusion constraint sql.
	 */
	protected dropExclusionConstraintSql(
		table: Table,
		exclusionOrName: TableExclusion | string,
	): Query {
		const exclusionName = InstanceChecker.isTableExclusion(exclusionOrName)
			? exclusionOrName.name
			: exclusionOrName;
		return new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${exclusionName}"`);
	}

	/**
	 * Builds create foreign key sql.
	 */
	protected createForeignKeySql(table: Table, foreignKey: TableForeignKey): Query {
		const columnNames = foreignKey.columnNames.map((column) => `"` + column + `"`).join(', ');
		const referencedColumnNames = foreignKey.referencedColumnNames
			.map((column) => `"` + column + `"`)
			.join(',');
		let sql =
			`ALTER TABLE ${this.escapePath(table)} ADD CONSTRAINT "${
				foreignKey.name
			}" FOREIGN KEY (${columnNames}) ` +
			`REFERENCES ${this.escapePath(this.getTablePath(foreignKey))}(${referencedColumnNames})`;
		if (foreignKey.onDelete) sql += ` ON DELETE ${foreignKey.onDelete}`;
		if (foreignKey.onUpdate) sql += ` ON UPDATE ${foreignKey.onUpdate}`;
		if (foreignKey.deferrable) sql += ` DEFERRABLE ${foreignKey.deferrable}`;

		return new Query(sql);
	}

	/**
	 * Builds drop foreign key sql.
	 */
	protected dropForeignKeySql(table: Table, foreignKeyOrName: TableForeignKey | string): Query {
		const foreignKeyName = InstanceChecker.isTableForeignKey(foreignKeyOrName)
			? foreignKeyOrName.name
			: foreignKeyOrName;
		return new Query(`ALTER TABLE ${this.escapePath(table)} DROP CONSTRAINT "${foreignKeyName}"`);
	}

	/**
	 * Builds sequence name from given table and column.
	 */
	protected buildSequenceName(table: Table, columnOrName: TableColumn | string): string {
		const { tableName } = this.driver.parseTableName(table);

		const columnName = InstanceChecker.isTableColumn(columnOrName)
			? columnOrName.name
			: columnOrName;

		let seqName = `${tableName}_${columnName}_seq`;

		if (seqName.length > this.connection.driver.maxAliasLength!) {
			// note doesn't yet handle corner cases where .length differs from number of UTF-8 bytes
			seqName = `${tableName.substring(0, 29)}_${columnName.substring(
				0,
				Math.max(29, 63 - table.name.length - 5),
			)}_seq`;
		}

		return seqName;
	}

	protected buildSequencePath(table: Table, columnOrName: TableColumn | string): string {
		const { schema } = this.driver.parseTableName(table);

		return schema
			? `${schema}.${this.buildSequenceName(table, columnOrName)}`
			: this.buildSequenceName(table, columnOrName);
	}

	/**
	 * Builds ENUM type name from given table and column.
	 */
	protected buildEnumName(
		table: Table,
		column: TableColumn,
		withSchema: boolean = true,
		disableEscape?: boolean,
		toOld?: boolean,
	): string {
		const { schema, tableName } = this.driver.parseTableName(table);
		let enumName = column.enumName
			? column.enumName
			: `${tableName}_${column.name.toLowerCase()}_enum`;
		if (schema && withSchema) enumName = `${schema}.${enumName}`;
		if (toOld) enumName = enumName + '_old';
		return enumName
			.split('.')
			.map((i) => {
				return disableEscape ? i : `"${i.replace(/"/g, '""')}"`;
			})
			.join('.');
	}

	protected async getUserDefinedTypeName(table: Table, column: TableColumn) {
		let { schema, tableName: name } = this.driver.parseTableName(table);

		if (!schema) {
			schema = await this.getCurrentSchema();
		}

		const result = await this.query(
			`SELECT "udt_schema", "udt_name" ` +
				`FROM "information_schema"."columns" WHERE "table_schema" = $1 AND "table_name" = $2 AND "column_name"=$3`,
			[schema, name, column.name],
		);

		// docs: https://www.postgresql.org/docs/current/xtypes.html
		// When you define a new base type, PostgreSQL automatically provides support for arrays of that type.
		// The array type typically has the same name as the base type with the underscore character (_) prepended.
		// ----
		// so, we must remove this underscore character from enum type name
		let udtName = result[0]['udt_name'];
		if (udtName.indexOf('_') === 0) {
			udtName = udtName.substr(1, udtName.length);
		}
		return {
			schema: result[0]['udt_schema'],
			name: udtName,
		};
	}

	/**
	 * Escapes a given comment so it's safe to include in a query.
	 */
	protected escapeComment(comment?: string) {
		if (!comment || comment.length === 0) {
			return 'NULL';
		}

		comment = comment.replace(/'/g, "''").replace(/\u0000/g, ''); // Null bytes aren't allowed in comments

		return `'${comment}'`;
	}

	/**
	 * Escapes given table or view path.
	 */
	protected escapePath(target: Table | View | string): string {
		const { schema, tableName } = this.driver.parseTableName(target);

		if (schema && schema !== this.driver.searchSchema) {
			return `"${schema}"."${tableName.replace(/"/g, '""')}"`;
		}

		return `"${tableName.replace(/"/g, '""')}"`;
	}

	/**
	 * Get the table name with table schema
	 * Note: Without ' or "
	 */
	protected async getTableNameWithSchema(target: Table | string) {
		const tableName = InstanceChecker.isTable(target) ? target.name : target;
		if (tableName.indexOf('.') === -1) {
			const schemaResult = await this.query(`SELECT current_schema()`);
			const schema = schemaResult[0]['current_schema'];
			return `${schema}.${tableName}`;
		} else {
			return `${tableName.split('.')[0]}.${tableName.split('.')[1]}`;
		}
	}

	/**
	 * Builds a query for create column.
	 */
	protected buildCreateColumnSql(table: Table, column: TableColumn) {
		let c = '"' + column.name + '"';
		if (column.isGenerated === true && column.generationStrategy !== 'uuid') {
			if (column.generationStrategy === 'identity') {
				// Postgres 10+ Identity generated column
				const generatedIdentityOrDefault = column.generatedIdentity || 'BY DEFAULT';
				c += ` ${column.type} GENERATED ${generatedIdentityOrDefault} AS IDENTITY`;
			} else {
				// classic SERIAL primary column
				if (column.type === 'integer' || column.type === 'int' || column.type === 'int4')
					c += ' SERIAL';
				if (column.type === 'smallint' || column.type === 'int2') c += ' SMALLSERIAL';
				if (column.type === 'bigint' || column.type === 'int8') c += ' BIGSERIAL';
			}
		}
		if (column.type === 'enum' || column.type === 'simple-enum') {
			c += ' ' + this.buildEnumName(table, column);
			if (column.isArray) c += ' array';
		} else if (!column.isGenerated || column.type === 'uuid') {
			c += ' ' + this.connection.driver.createFullType(column);
		}

		// Postgres only supports the stored generated column type
		if (column.generatedType === 'STORED' && column.asExpression) {
			c += ` GENERATED ALWAYS AS (${column.asExpression}) STORED`;
		}

		if (column.charset) c += ' CHARACTER SET "' + column.charset + '"';
		if (column.collation) c += ' COLLATE "' + column.collation + '"';
		if (column.isNullable !== true) c += ' NOT NULL';
		if (column.default !== undefined && column.default !== null) c += ' DEFAULT ' + column.default;
		if (column.isGenerated && column.generationStrategy === 'uuid' && !column.default)
			c += ` DEFAULT ${this.driver.uuidGenerator}`;

		return c;
	}

	/**
	 * Checks if the PostgreSQL server has support for partitioned tables
	 */
	protected async hasSupportForPartitionedTables() {
		const result = await this.query(
			`SELECT TRUE FROM information_schema.columns WHERE table_name = 'pg_class' and column_name = 'relispartition'`,
		);
		return result.length ? true : false;
	}

	/**
	 * Change table comment.
	 */
	async changeTableComment(tableOrName: Table | string, newComment?: string): Promise<void> {
		const upQueries: Query[] = [];
		const downQueries: Query[] = [];

		const table = InstanceChecker.isTable(tableOrName)
			? tableOrName
			: await this.getCachedTable(tableOrName);

		newComment = this.escapeComment(newComment);
		const comment = this.escapeComment(table.comment);

		if (newComment === comment) {
			return;
		}

		const newTable = table.clone();

		upQueries.push(new Query(`COMMENT ON TABLE ${this.escapePath(newTable)} IS ${newComment}`));

		downQueries.push(new Query(`COMMENT ON TABLE ${this.escapePath(table)} IS ${comment}`));

		await this.executeQueries(upQueries, downQueries);

		table.comment = newTable.comment;
		this.replaceCachedTable(table, newTable);
	}
}