sql_table.ts

// deno-lint-ignore-file

import {debugAssert} from "./debug_assert.ts";
import {mysql, Sql} from "./sql.ts";
import
{	SqlSettings,
	SqlMode,
	DEFAULT_SETTINGS_MYSQL, DEFAULT_SETTINGS_MYSQL_ONLY,
	DEFAULT_SETTINGS_PGSQL, DEFAULT_SETTINGS_PGSQL_ONLY,
	DEFAULT_SETTINGS_SQLITE, DEFAULT_SETTINGS_SQLITE_ONLY,
	DEFAULT_SETTINGS_MSSQL, DEFAULT_SETTINGS_MSSQL_ONLY,
} from './sql_settings.ts';

type Join = {tableName: string, alias: string, onExpr: string|Sql, isLeft: boolean};
export type OrderBy = string | Sql | {columns: string[], desc?: boolean};

export const mysqlTables: Record<string, SqlTable> = new Proxy
(	{},
	{	get(target, tableName)
		{	if (typeof(tableName) != 'string')
			{	throw new Error("Table name must be string");
			}
			return new SqlTable(DEFAULT_SETTINGS_MYSQL, tableName);
		}
	}
);

export const mysqlOnlyTables: Record<string, SqlTable> = new Proxy
(	{},
	{	get(target, tableName)
		{	if (typeof(tableName) != 'string')
			{	throw new Error("Table name must be string");
			}
			return new SqlTable(DEFAULT_SETTINGS_MYSQL_ONLY, tableName);
		}
	}
);

export const pgsqlTables: Record<string, SqlTable> = new Proxy
(	{},
	{	get(target, tableName)
		{	if (typeof(tableName) != 'string')
			{	throw new Error("Table name must be string");
			}
			return new SqlTable(DEFAULT_SETTINGS_PGSQL, tableName);
		}
	}
);

export const pgsqlOnlyTables: Record<string, SqlTable> = new Proxy
(	{},
	{	get(target, tableName)
		{	if (typeof(tableName) != 'string')
			{	throw new Error("Table name must be string");
			}
			return new SqlTable(DEFAULT_SETTINGS_PGSQL_ONLY, tableName);
		}
	}
);

export const sqliteTables: Record<string, SqlTable> = new Proxy
(	{},
	{	get(target, tableName)
		{	if (typeof(tableName) != 'string')
			{	throw new Error("Table name must be string");
			}
			return new SqlTable(DEFAULT_SETTINGS_SQLITE, tableName);
		}
	}
);

export const sqliteOnlyTables: Record<string, SqlTable> = new Proxy
(	{},
	{	get(target, tableName)
		{	if (typeof(tableName) != 'string')
			{	throw new Error("Table name must be string");
			}
			return new SqlTable(DEFAULT_SETTINGS_SQLITE_ONLY, tableName);
		}
	}
);

export const mssqlTables: Record<string, SqlTable> = new Proxy
(	{},
	{	get(target, tableName)
		{	if (typeof(tableName) != 'string')
			{	throw new Error("Table name must be string");
			}
			return new SqlTable(DEFAULT_SETTINGS_MSSQL, tableName);
		}
	}
);

export const mssqlOnlyTables: Record<string, SqlTable> = new Proxy
(	{},
	{	get(target, tableName)
		{	if (typeof(tableName) != 'string')
			{	throw new Error("Table name must be string");
			}
			return new SqlTable(DEFAULT_SETTINGS_MSSQL_ONLY, tableName);
		}
	}
);

const enum Operation
{	NONE,
	INSERT,
	INSERT_SELECT,
	SELECT,
	UPDATE,
	DELETE,
	TRUNCATE,
}

export class SqlTable extends Sql
{	private joins: Join[] = [];
	private whereExprs: (string | Sql)[] = [];
	private groupByExprs: string|string[]|Sql|undefined;
	private havingExpr: string|Sql = '';

	private hasB = false;
	private hasBase = false;
	private hasBaseTable = false;
	private hasS = false;
	private hasSubj = false;
	private hasSubjTable = false;

	private operation = Operation.NONE;
	private operationInsertRows: Iterable<Record<string, any>> | undefined;
	private operationInsertOnConflictDo: ''|'nothing'|'replace'|'update'|'patch' = '';
	private operationInsertNames: string[] | undefined;
	private operationInsertSelect: Sql | undefined;
	private operationSelectColumns: string|string[]|Sql = '';
	private operationSelectOrderBy: OrderBy = '';
	private operationSelectOffset = 0;
	private operationSelectLimit = 0;
	private operationUpdateRow: Record<string, any> | undefined;

	constructor
	(	sqlSettings: SqlSettings,
		public tableName: string,
		strings?: string[],
		params?: any[]
	)
	{	super(sqlSettings, strings, params);
		this.tableUsed(tableName);
	}

	private getBaseTableAlias()
	{	return this.joins.length==0 ? '' : !this.hasB ? 'b' : !this.hasBase ? 'base' : !this.hasBaseTable ? 'base_table' : '_base_table';
	}

	private getSubjTableAlias()
	{	return !this.hasS ? 's' : !this.hasSubj ? 'subj' : !this.hasSubjTable ? 'subj_table' : '_subj_table';
	}

	private tableUsed(alias: string)
	{	alias = alias.toLowerCase();
		if (alias == 'b')
		{	this.hasB = true;
		}
		else if (alias == 'base')
		{	this.hasBase = true;
		}
		else if (alias == 'base_table')
		{	this.hasBaseTable = true;
		}
		else if (alias == '_base_table')
		{	throw new Error(`Alias "_base_table" is reserved`);
		}
		else if (alias == 's')
		{	this.hasS = true;
		}
		else if (alias == 'subj')
		{	this.hasSubj = true;
		}
		else if (alias == 'subj_table')
		{	this.hasSubjTable = true;
		}
		else if (alias == '_subj_table')
		{	throw new Error(`Alias "_subj_table" is reserved`);
		}
	}

	private appendJoins(baseTable: string)
	{	this.strings[this.strings.length - 1] += ' ';
		this.estimatedByteLength++;
		this.appendTableName(this.tableName);
		if (this.joins.length != 0)
		{	this.append(mysql` AS "${baseTable}"`);
			for (let {tableName, alias, onExpr, isLeft} of this.joins)
			{	if (!onExpr)
				{	this.strings[this.strings.length - 1] += ' CROSS JOIN ';
					this.estimatedByteLength += 12;
					this.appendTableName(tableName);
					if (alias)
					{	this.append(mysql` AS "${alias}"`);
					}
				}
				else if (!isLeft)
				{	this.strings[this.strings.length - 1] += ' INNER JOIN ';
					this.estimatedByteLength += 12;
					this.appendTableName(tableName);
					this.append(!alias ? mysql` ON (${baseTable}.${onExpr})` : mysql` AS "${alias}" ON (${baseTable}.${onExpr})`);
				}
				else
				{	this.strings[this.strings.length - 1] += ' LEFT JOIN ';
					this.estimatedByteLength += 11;
					this.appendTableName(tableName);
					this.append(!alias ? mysql` ON (${baseTable}.${onExpr})` : mysql` AS "${alias}" ON (${baseTable}.${onExpr})`);
				}
			}
		}
	}

	private appendJoinsExceptFirst(baseTable: string)
	{	let {tableName, alias} = this.joins[0];
		this.append(!alias ? mysql` "${tableName}"` : mysql` "${tableName}" AS "${alias}"`);
		for (let i=1, iEnd=this.joins.length; i<iEnd; i++)
		{	let {tableName, alias, onExpr, isLeft} = this.joins[i];
			if (!onExpr)
				{	this.strings[this.strings.length - 1] += ' CROSS JOIN ';
					this.estimatedByteLength += 12;
					this.appendTableName(tableName);
					if (alias)
					{	this.append(mysql` AS "${alias}"`);
					}
				}
				else if (!isLeft)
				{	this.strings[this.strings.length - 1] += ' INNER JOIN ';
					this.estimatedByteLength += 12;
					this.appendTableName(tableName);
					this.append(!alias ? mysql` ON (${baseTable}.${onExpr})` : mysql` AS "${alias}" ON (${baseTable}.${onExpr})`);
				}
				else
				{	this.strings[this.strings.length - 1] += ' LEFT JOIN ';
					this.estimatedByteLength += 11;
					this.appendTableName(tableName);
					this.append(!alias ? mysql` ON (${baseTable}.${onExpr})` : mysql` AS "${alias}" ON (${baseTable}.${onExpr})`);
				}
		}
	}

	private appendWhereExprs(baseTable: string)
	{	if (this.whereExprs.length == 0)
		{	throw new Error(`Please, call where() first`);
		}
		let hasWhere = false;
		for (let whereExpr of this.whereExprs)
		{	if (whereExpr)
			{	this.append(!hasWhere ? mysql` WHERE (${baseTable}.${whereExpr})` : mysql` AND (${baseTable}.${whereExpr})`);
				hasWhere = true;
			}
		}
		return hasWhere;
	}

	private someJoin(tableName: string, alias: string, onExpr: string|Sql, isLeft: boolean)
	{	if (this.whereExprs.length)
		{	throw new Error(`join() can be called before where()`);
		}
		if (this.groupByExprs != undefined)
		{	throw new Error(`join() can be called before groupBy()`);
		}
		this.joins.push({tableName, alias, onExpr, isLeft});
		this.tableUsed(alias || tableName);
	}

	/**	Adds an INNER (if `onExpr` is given) or a CROSS join (if `onExpr` is blank).
		This method can be called multiple times.
		The method returns a new `SqlTable` object that has everything from the original object, plus the new join.
	 **/
	join(tableName: string, alias='', onExpr: string|Sql='')
	{	this.someJoin(tableName, alias, onExpr, false);
		return this;
	}

	/**	Adds a LEFT JOIN.
		This method can be called multiple times.
		The method returns a new `SqlTable` object that has everything from the original object, plus the new join.
	 **/
	leftJoin(tableName: string, alias: string, onExpr: string|Sql)
	{	if (!onExpr)
		{	throw new Error(`No condition in LEFT JOIN`);
		}
		this.someJoin(tableName, alias, onExpr, true);
		return this;
	}

	/**	Adds WHERE condition for SELECT, UPDATE and DELETE queries.
		The method returns a new `SqlTable` object that has everything from the original object, plus the new condition.
		You can call `sqlTable.select()`, `sqlTable.update()` and `sqlTable.delete()` only after calling `sqlTable.where()`, or an exception will be thrown.
		To explicitly allow working on the whole table, call `sqlTable.where('')` (with empty condition).
	 **/
	where(whereExpr: string|Sql)
	{	if (this.groupByExprs != undefined)
		{	throw new Error(`where() can be called before groupBy()`);
		}
		this.whereExprs.push(whereExpr);
		return this;
	}

	/**	Adds GROUP BY expressions, and optionally a HAVING expression to the SELECT query.
		If `groupByExprs` is a string or an `Sql` object, it will represent a safe SQL fragment that contains comma-separated list of column expressions.
		If it's `string[]`, it will be treated as array of column names.
	 **/
	groupBy(groupByExprs: string|string[]|Sql, havingExpr: string|Sql='')
	{	if (this.groupByExprs != undefined)
		{	throw new Error(`groupBy() can be called only once`);
		}
		this.groupByExprs = groupByExprs;
		this.havingExpr = havingExpr;
		return this;
	}

	/**	This function is called every time a quoted table name must be appended to the query.
		Subclasses can override this function to convert table names and maybe add schema prefixes.
		The query generation starts when this object is asked to be converted to string or to bytes,
		so this function will not be called before this.
		This function must then return the converted table name without qualifiers.
		Default implementation:

		```
		this.append(sql`"${tableName}"`);
		return tableName;
		```
	 **/
	protected appendTableName(tableName: string)
	{	this.append(mysql`"${tableName}"`);
		return tableName;
	}

	/**	Generates an INSERT query.
		- `onConflictDo=='nothing'` is only supported for MySQL, PostgreSQL and SQLite. Ignores (doesn't insert) conflicting rows (if unique constraint fails).
		- `onConflictDo=='replace'` is only supported for MySQL and SQLite.
		- `onConflictDo=='update'` is only supported for MySQL. If duplicate key, updates the existing record with the new values.
		- `onConflictDo=='patch'` is only supported for MySQL If duplicate key, updates **empty** (null, 0 or '') columns of the existing record with the new values.
	 **/
	insert(rows: Iterable<Record<string, any>>, onConflictDo: ''|'nothing'|'replace'|'update'|'patch' = '')
	{	if (this.joins.length)
		{	throw new Error(`Cannot INSERT with JOIN`);
		}
		if (this.whereExprs.length)
		{	throw new Error(`Cannot INSERT with WHERE`);
		}
		if (this.groupByExprs != undefined)
		{	throw new Error(`Cannot INSERT with GROUP BY`);
		}
		this.operation = Operation.INSERT;
		this.operationInsertRows = rows;
		this.operationInsertOnConflictDo = onConflictDo;
		return this;
	}

	/**	Generates "INSERT INTO (...) SELECT ..." query.

		import {mysqlTables as sqlTables} from 'https://deno.land/x/polysql/mod.ts';

		let s = sqlTables.t_log.insertFrom(['c1', 'c2'], sqlTables.t_log_bak.where('id<=100').select(['c1', 'c2']));
		console.log('' + s); // prints: INSERT INTO `t_log` (`c1`, `c2`) SELECT `c1`, `c2` FROM `t_log_bak` WHERE (`id`<=100)
	 **/
	insertFrom(names: string[], select: Sql, onConflictDo: ''|'nothing'|'replace' = '')
	{	if (this.joins.length)
		{	throw new Error(`Cannot INSERT with JOIN`);
		}
		if (this.whereExprs.length)
		{	throw new Error(`Cannot INSERT with WHERE`);
		}
		if (this.groupByExprs != undefined)
		{	throw new Error(`Cannot INSERT with GROUP BY`);
		}
		this.operation = Operation.INSERT_SELECT;
		this.operationInsertNames = names;
		this.operationInsertSelect = select;
		this.operationInsertOnConflictDo = onConflictDo;
		return this;
	}

	/**	Generates a SELECT query.
		If `columns` parameter is a string or an `Sql` object, it will represent columns as a safe SQL fragment.
		If it's `string[]`, it will be treated as array of column names.
		Empty string or array will represent `*`-wildcard (select all columns).
		OFFSET and LIMIT without ORDER BY are not supported on Microsoft SQL Server.
	 **/
	select(columns: string|string[]|Sql='', orderBy: OrderBy='', offset=0, limit=0)
	{	this.operation = Operation.SELECT;
		this.operationSelectColumns = columns;
		this.operationSelectOrderBy = orderBy;
		this.operationSelectOffset = offset;
		this.operationSelectLimit = limit;
		return this;
	}

	/**	Generates an UPDATE query. You can update with joins, but if the first join is a LEFT JOIN, such query is not supported by PostgreSQL.
		Columns of the base table (not joined) will be updated.
	 **/
	update(row: Record<string, any>)
	{	if (this.groupByExprs != undefined)
		{	throw new Error(`Cannot UPDATE with GROUP BY`);
		}
		this.operation = Operation.UPDATE;
		this.operationUpdateRow = row;
		return this;
	}

	/**	Generates a DELETE query. You can delete with joins, but if the first join is a LEFT JOIN, such query is not supported by PostgreSQL.
		Will delete from the base table (not joined).
	 **/
	delete()
	{	if (this.groupByExprs != undefined)
		{	throw new Error(`Cannot DELETE with GROUP BY`);
		}
		this.operation = Operation.DELETE;
		return this;
	}

	truncate()
	{	if (this.joins.length)
		{	throw new Error(`Cannot TRUNCATE with JOIN`);
		}
		if (this.whereExprs.length)
		{	throw new Error(`Cannot TRUNCATE with WHERE`);
		}
		if (this.groupByExprs != undefined)
		{	throw new Error(`Cannot TRUNCATE with GROUP BY`);
		}
		this.operation = Operation.TRUNCATE;
		return this;
	}

	encode(putParamsTo?: any[], mysqlNoBackslashEscapes=false, useBuffer?: Uint8Array, useBufferFromPos=0, defaultParentName?: Uint8Array): Uint8Array
	{	this.doOperation();
		return super.encode(putParamsTo, mysqlNoBackslashEscapes, useBuffer, useBufferFromPos, defaultParentName);
	}

	private doOperation()
	{	let afterSelect: Sql | undefined;

		switch (this.operation)
		{	case Operation.INSERT:
			{	let rows = this.operationInsertRows!;
				let onConflictDo = this.operationInsertOnConflictDo;
				if (!onConflictDo)
				{	this.strings[this.strings.length - 1] += 'INSERT INTO ';
					this.estimatedByteLength += 12;
					this.appendTableName(this.tableName);
					this.append(mysql` <${rows}>`);
				}
				else if (onConflictDo == 'nothing')
				{	let {mode} = this.sqlSettings;
					switch (mode)
					{	case SqlMode.MYSQL:
							throw new Error("ON CONFLICT DO NOTHING is not supported across all engines. Please use mysqlOnly`...`");

						case SqlMode.PGSQL:
							throw new Error("ON CONFLICT DO NOTHING is not supported across all engines. Please use pgsqlOnly`...`");

						case SqlMode.SQLITE:
							throw new Error("ON CONFLICT DO NOTHING is not supported across all engines. Please use sqliteOnly`...`");

						case SqlMode.MSSQL:
						case SqlMode.MSSQL_ONLY:
							throw new Error("ON CONFLICT DO NOTHING is not supported on MS SQL");

						case SqlMode.MYSQL_ONLY:
						{	let {names, rows: rowsW} = wrapRowsIterator(rows);
							this.strings[this.strings.length - 1] += 'INSERT INTO ';
							this.estimatedByteLength += 12;
							this.appendTableName(this.tableName);
							this.append(mysql` <${rowsW}> ON DUPLICATE KEY UPDATE "${names[0]}"="${names[0]}"`);
							break;
						}

						default:
							debugAssert(mode==SqlMode.PGSQL_ONLY || mode==SqlMode.SQLITE_ONLY);
							this.strings[this.strings.length - 1] += 'INSERT INTO ';
							this.estimatedByteLength += 12;
							this.appendTableName(this.tableName);
							this.append(mysql` <${rows}> ON CONFLICT DO NOTHING`);
					}
				}
				else if (onConflictDo == 'replace')
				{	switch (this.sqlSettings.mode)
					{	case SqlMode.MYSQL:
							throw new Error("REPLACE is not supported across all engines. Please use mysqlOnly`...`");

						case SqlMode.SQLITE:
							throw new Error("REPLACE is not supported across all engines. Please use sqliteOnly`...`");

						case SqlMode.PGSQL:
						case SqlMode.PGSQL_ONLY:
							throw new Error("REPLACE is not supported on PostgreSQL");

						case SqlMode.MSSQL:
						case SqlMode.MSSQL_ONLY:
							throw new Error("REPLACE is not supported on MS SQL");

						case SqlMode.MYSQL_ONLY:
							this.strings[this.strings.length - 1] += 'REPLACE ';
							this.estimatedByteLength += 8;
							this.appendTableName(this.tableName);
							this.append(mysql` <${rows}>`);
							break;

						default:
							debugAssert(this.sqlSettings.mode == SqlMode.SQLITE_ONLY);
							this.strings[this.strings.length - 1] += 'REPLACE INTO ';
							this.estimatedByteLength += 13;
							this.appendTableName(this.tableName);
							this.append(mysql` <${rows}>`);
					}
				}
				else
				{	debugAssert(onConflictDo=='update' || onConflictDo=='patch');
					let isPatch = onConflictDo == 'patch';
					switch (this.sqlSettings.mode)
					{	case SqlMode.MYSQL:
							throw new Error("ON CONFLICT DO UPDATE is not supported across all engines. Please use mysqlOnly`...`");

						case SqlMode.SQLITE:
						case SqlMode.SQLITE_ONLY:
							throw new Error("ON CONFLICT DO UPDATE is not supported on SQLite");

						case SqlMode.PGSQL:
						case SqlMode.PGSQL_ONLY:
							throw new Error("ON CONFLICT DO UPDATE is not supported on PostgreSQL");

						case SqlMode.MSSQL:
						case SqlMode.MSSQL_ONLY:
							throw new Error("ON CONFLICT DO UPDATE is not supported on MS SQL");

						default:
						{	debugAssert(this.sqlSettings.mode == SqlMode.MYSQL_ONLY);
							let {names, rows: rowsW} = wrapRowsIterator(rows);
							this.strings[this.strings.length - 1] += 'INSERT INTO ';
							this.estimatedByteLength += 12;
							let tableName = this.appendTableName(this.tableName);
							this.append(mysql` <${rowsW}> AS excluded ON DUPLICATE KEY UPDATE `);
							let wantComma = false;
							for (let name of names)
							{	if (wantComma)
								{	this.append(mysql`, `);
								}
								wantComma = true;
								if (!isPatch)
								{	this.append(mysql`"${name}"=excluded."${name}"`);
								}
								else
								{	this.append(mysql`"${name}"=CASE WHEN excluded."${name}" IS NOT NULL AND ("${tableName}"."${name}" IS NULL OR Cast(excluded."${name}" AS char) NOT IN ('', '0') OR Cast("${tableName}"."${name}" AS char) IN ('', '0')) THEN excluded."${name}" ELSE "${tableName}"."${name}" END`);
								}
							}
							break;
						}
					}
				}
				break;
			}

			case Operation.INSERT_SELECT:
			{	let names = this.operationInsertNames!;
				let select = this.operationInsertSelect!;
				let onConflictDo = this.operationInsertOnConflictDo;
				if (!onConflictDo)
				{	this.strings[this.strings.length - 1] += 'INSERT INTO ';
					this.estimatedByteLength += 12;
				}
				else if (onConflictDo == 'nothing')
				{	let {mode} = this.sqlSettings;
					switch (mode)
					{	case SqlMode.MYSQL:
							throw new Error("ON CONFLICT DO NOTHING is not supported across all engines. Please use mysqlOnly`...`");

						case SqlMode.PGSQL:
							throw new Error("ON CONFLICT DO NOTHING is not supported across all engines. Please use pgsqlOnly`...`");

						case SqlMode.SQLITE:
							throw new Error("ON CONFLICT DO NOTHING is not supported across all engines. Please use sqliteOnly`...`");

						case SqlMode.MSSQL:
						case SqlMode.MSSQL_ONLY:
							throw new Error("ON CONFLICT DO NOTHING is not supported on MS SQL");

						case SqlMode.MYSQL_ONLY:
							this.strings[this.strings.length - 1] += 'INSERT INTO ';
							this.estimatedByteLength += 12;
							afterSelect = mysql` ON DUPLICATE KEY UPDATE "${names[0]}"="${names[0]}"`;
							break;

						default:
							debugAssert(mode==SqlMode.PGSQL_ONLY || mode==SqlMode.SQLITE_ONLY);
							this.strings[this.strings.length - 1] += 'INSERT INTO ';
							this.estimatedByteLength += 12;
							afterSelect = mysql` ON CONFLICT DO NOTHING`;
					}
				}
				else
				{	debugAssert(onConflictDo == 'replace');
					switch (this.sqlSettings.mode)
					{	case SqlMode.MYSQL:
							throw new Error("REPLACE is not supported across all engines. Please use mysqlOnly`...`");

						case SqlMode.SQLITE:
							throw new Error("REPLACE is not supported across all engines. Please use sqliteOnly`...`");

						case SqlMode.PGSQL:
						case SqlMode.PGSQL_ONLY:
							throw new Error("REPLACE is not supported on PostgreSQL");

						case SqlMode.MSSQL:
						case SqlMode.MSSQL_ONLY:
							throw new Error("REPLACE is not supported on MS SQL");

						case SqlMode.MYSQL_ONLY:
							this.strings[this.strings.length - 1] += 'REPLACE ';
							this.estimatedByteLength += 8;
							break;

						default:
							debugAssert(this.sqlSettings.mode == SqlMode.SQLITE_ONLY);
							this.strings[this.strings.length - 1] += 'REPLACE INTO ';
							this.estimatedByteLength += 13;
					}
				}
				this.appendTableName(this.tableName);
				this.append(mysql` ("${names}+") `);
				if (!(select instanceof SqlTable) || select.operation!=Operation.SELECT)
				{	this.append(select);
					if (afterSelect)
					{	this.append(afterSelect);
					}
					break;
				}
				this.tableName = select.tableName;
				this.joins = select.joins;
				this.whereExprs = select.whereExprs;
				this.groupByExprs = select.groupByExprs;
				this.havingExpr = select.havingExpr;
				this.operationSelectColumns = select.operationSelectColumns;
				this.operationSelectOrderBy = select.operationSelectOrderBy;
				this.operationSelectOffset = select.operationSelectOffset;
				this.operationSelectLimit = select.operationSelectLimit;
				// fallthrough to Operation.SELECT
			}

			case Operation.SELECT:
			{	let columns = this.operationSelectColumns;
				let orderBy = this.operationSelectOrderBy;
				let offset = this.operationSelectOffset;
				let limit = this.operationSelectLimit;
				let baseTable = this.getBaseTableAlias();
				if (!columns)
				{	this.append(mysql`SELECT * FROM`);
				}
				else if (Array.isArray(columns))
				{	this.append(mysql`SELECT "${baseTable}.${columns}*" FROM`);
				}
				else
				{	this.append(mysql`SELECT ${baseTable}.${columns} FROM`);
				}
				this.appendJoins(baseTable);
				this.appendWhereExprs(baseTable);
				if (this.groupByExprs)
				{	if (!Array.isArray(this.groupByExprs))
					{	this.append(mysql` GROUP BY ${baseTable}.${this.groupByExprs}`);
					}
					else if (this.groupByExprs.length)
					{	this.append(mysql` GROUP BY "${baseTable}.${this.groupByExprs}+"`);
					}
					if (this.havingExpr)
					{	this.append(mysql` HAVING (${this.havingExpr})`);
					}
				}
				let hasOrderBy = false;
				if (orderBy)
				{	if (typeof(orderBy)=='string' || (orderBy instanceof Sql))
					{	this.append(mysql` ORDER BY ${orderBy}`);
						hasOrderBy = true;
					}
					else
					{	let {columns, desc} = orderBy;
						let nColumns = columns.length;
						hasOrderBy = nColumns != 0;
						if (hasOrderBy)
						{	if (!desc)
							{	this.append(mysql` ORDER BY "${columns}+"`);
							}
							else
							{	this.append(mysql` ORDER BY "${columns[0]}" DESC`);
								for (let i=1; i<nColumns; i++)
								{	this.append(mysql`, "${columns[i]}" DESC`);
								}
							}
						}
					}
				}
				if (limit > 0)
				{	switch (this.sqlSettings.mode)
					{	case SqlMode.MYSQL:
							if (!hasOrderBy)
							{	throw new Error("SELECT with LIMIT but without ORDER BY is not supported across all engines. Please use mysqlOnly`...`");
							}
						case SqlMode.MYSQL_ONLY:
							this.append(offset>0 ? mysql` LIMIT '${limit}' OFFSET '${offset}'` : mysql` LIMIT '${limit}'`);
							break;

						case SqlMode.PGSQL:
							if (!hasOrderBy)
							{	throw new Error("SELECT with LIMIT but without ORDER BY is not supported across all engines. Please use pgsqlOnly`...`");
							}
						case SqlMode.PGSQL_ONLY:
							this.append(offset>0 ? mysql` LIMIT '${limit}' OFFSET '${offset}'` : mysql` LIMIT '${limit}'`);
							break;

						case SqlMode.SQLITE:
							if (!hasOrderBy)
							{	throw new Error("SELECT with LIMIT but without ORDER BY is not supported across all engines. Please use sqliteOnly`...`");
							}
						case SqlMode.SQLITE_ONLY:
							this.append(offset>0 ? mysql` LIMIT '${limit}' OFFSET '${offset}'` : mysql` LIMIT '${limit}'`);
							break;

						default:
							debugAssert(this.sqlSettings.mode==SqlMode.MSSQL || this.sqlSettings.mode==SqlMode.MSSQL_ONLY);
							if (!hasOrderBy)
							{	throw new Error("SELECT with LIMIT but without ORDER BY is not supported on MS SQL");
							}
							this.append(mysql` OFFSET '${offset}' ROWS FETCH FIRST '${limit}' ROWS ONLY`);
					}
				}
				else if (offset > 0)
				{	switch (this.sqlSettings.mode)
					{	case SqlMode.MYSQL:
							if (!hasOrderBy)
							{	throw new Error("SELECT with OFFSET but without ORDER BY is not supported across all engines. Please use mysqlOnly`...`");
							}
						case SqlMode.MYSQL_ONLY:
							this.append(mysql` LIMIT 2147483647 OFFSET '${offset}'`);
							break;

						case SqlMode.PGSQL:
							if (!hasOrderBy)
							{	throw new Error("SELECT with OFFSET but without ORDER BY is not supported across all engines. Please use pgsqlOnly`...`");
							}
						case SqlMode.PGSQL_ONLY:
							this.append(mysql` OFFSET '${offset}'`);
							break;

						case SqlMode.SQLITE:
							if (!hasOrderBy)
							{	throw new Error("SELECT with OFFSET but without ORDER BY is not supported across all engines. Please use sqliteOnly`...`");
							}
						case SqlMode.SQLITE_ONLY:
							this.append(mysql` LIMIT 2147483647 OFFSET '${offset}'`);
							break;

						default:
							debugAssert(this.sqlSettings.mode==SqlMode.MSSQL || this.sqlSettings.mode==SqlMode.MSSQL_ONLY);
							if (!hasOrderBy)
							{	throw new Error("SELECT with OFFSET but without ORDER BY is not supported on MS SQL");
							}
							this.append(mysql` OFFSET '${offset}' ROWS`);
					}
				}
				if (afterSelect)
				{	this.append(afterSelect);
				}
				break;
			}

			case Operation.UPDATE:
			{	let row = this.operationUpdateRow!;
				let {mode} = this.sqlSettings;
				if (this.joins.length == 0)
				{	this.strings[this.strings.length - 1] += 'UPDATE ';
					this.estimatedByteLength += 7;
					this.appendTableName(this.tableName);
					this.append(mysql` SET {${row}}`);
					this.appendWhereExprs('');
				}
				else
				{	let baseTable = this.getBaseTableAlias();
					let [{onExpr, isLeft}] = this.joins;
					if (isLeft)
					{	switch (mode)
						{	case SqlMode.MYSQL:
								throw new Error("UPDATE where the first join is a LEFT JOIN is not supported across all engines. Please use mysqlOnly`...`");
							case SqlMode.SQLITE:
								throw new Error("UPDATE where the first join is a LEFT JOIN is not supported across all engines. Please use sqliteOnly`...`");
							case SqlMode.MSSQL:
								throw new Error("UPDATE where the first join is a LEFT JOIN is not supported across all engines. Please use mssqlOnly`...`");
							case SqlMode.PGSQL:
							case SqlMode.PGSQL_ONLY:
								throw new Error("UPDATE where the first join is a LEFT JOIN is not supported on PostgreSQL");
						}
					}
					switch (mode)
					{	case SqlMode.MYSQL:
						case SqlMode.MYSQL_ONLY:
						{	this.strings[this.strings.length - 1] += 'UPDATE';
							this.estimatedByteLength += 6;
							this.appendJoins(baseTable);
							this.append(mysql` SET {${baseTable}.${row}}`);
							this.appendWhereExprs(baseTable);
							break;
						}

						case SqlMode.SQLITE_ONLY:
							if (isLeft)
							{	let subj = this.getSubjTableAlias();
								this.strings[this.strings.length - 1] += 'UPDATE ';
								this.estimatedByteLength += 7;
								this.appendTableName(this.tableName);
								this.append(mysql` AS "${subj}" SET {.${baseTable}.${row}} FROM`);
								this.appendJoins(baseTable);
								let hasWhere = this.appendWhereExprs(baseTable);
								this.append(hasWhere ? mysql` AND "${subj}".rowid = "${baseTable}".rowid` : mysql` WHERE "${subj}".rowid = "${baseTable}".rowid`);
								break;
							}
							// fallthrough

						case SqlMode.PGSQL:
						case SqlMode.PGSQL_ONLY:
						case SqlMode.SQLITE:
						{	this.strings[this.strings.length - 1] += 'UPDATE ';
							this.estimatedByteLength += 7;
							this.appendTableName(this.tableName);
							this.append(mysql` AS "${baseTable}" SET {.${baseTable}.${row}} FROM`);
							this.appendJoinsExceptFirst(baseTable);
							let hasWhere = this.appendWhereExprs(baseTable);
							this.append(hasWhere ? mysql` AND (${baseTable}.${onExpr})` : mysql` WHERE (${baseTable}.${onExpr})`);
							break;
						}

						default:
						{	debugAssert(mode==SqlMode.MSSQL || mode==SqlMode.MSSQL_ONLY);
							this.strings[this.strings.length - 1] += 'UPDATE ';
							this.estimatedByteLength += 7;
							this.appendTableName(this.tableName);
							this.append(mysql` SET {.${baseTable}.${row}} FROM`);
							this.appendJoins(baseTable);
							this.appendWhereExprs(baseTable);
						}
					}
				}
				break;
			}

			case Operation.DELETE:
			{	let {mode} = this.sqlSettings;
				if (this.joins.length == 0)
				{	this.strings[this.strings.length - 1] += 'DELETE FROM ';
					this.estimatedByteLength += 12;
					this.appendTableName(this.tableName);
					this.appendWhereExprs('');
				}
				else
				{	let baseTable = this.getBaseTableAlias();
					let [{onExpr, isLeft}] = this.joins;
					if (isLeft)
					{	switch (mode)
						{	case SqlMode.MYSQL:
								throw new Error("DELETE where the first join is a LEFT JOIN is not supported across all engines. Please use mysqlOnly`...`");
							case SqlMode.SQLITE:
								throw new Error("DELETE where the first join is a LEFT JOIN is not supported across all engines. Please use sqliteOnly`...`");
							case SqlMode.MSSQL:
								throw new Error("DELETE where the first join is a LEFT JOIN is not supported across all engines. Please use mssqlOnly`...`");
							case SqlMode.PGSQL:
							case SqlMode.PGSQL_ONLY:
								throw new Error("DELETE where the first join is a LEFT JOIN is not supported on PostgreSQL");
						}
					}
					switch (mode)
					{	case SqlMode.MYSQL:
						case SqlMode.MYSQL_ONLY:
						case SqlMode.MSSQL:
						case SqlMode.MSSQL_ONLY:
						{	this.append(mysql`DELETE "${baseTable}" FROM`);
							this.appendJoins(baseTable);
							this.appendWhereExprs(baseTable);
							break;
						}

						case SqlMode.PGSQL:
						case SqlMode.PGSQL_ONLY:
						{	this.strings[this.strings.length - 1] += 'DELETE FROM ';
							this.estimatedByteLength += 12;
							this.appendTableName(this.tableName);
							this.append(mysql` AS "${baseTable}" USING`);
							this.appendJoinsExceptFirst(baseTable);
							let hasWhere = this.appendWhereExprs(baseTable);
							this.append(hasWhere ? mysql` AND (${baseTable}.${onExpr})` : mysql` WHERE (${baseTable}.${onExpr})`);
							break;
						}

						default:
						{	debugAssert(mode==SqlMode.SQLITE || mode==SqlMode.SQLITE_ONLY);
							let subj = this.getSubjTableAlias();
							this.strings[this.strings.length - 1] += 'DELETE FROM ';
							this.estimatedByteLength += 12;
							this.appendTableName(this.tableName);
							this.append(mysql` AS "${subj}" WHERE rowid IN (SELECT "${baseTable}".rowid FROM`);
							this.appendJoins(baseTable);
							this.appendWhereExprs(baseTable);
							this.append(mysql`)`);
						}
					}
				}
				break;
			}

			case Operation.TRUNCATE:
			{	switch (this.sqlSettings.mode)
				{	case SqlMode.MYSQL:
					case SqlMode.MYSQL_ONLY:
					case SqlMode.PGSQL:
					case SqlMode.PGSQL_ONLY:
					case SqlMode.MSSQL:
					case SqlMode.MSSQL_ONLY:
						this.strings[this.strings.length - 1] += 'TRUNCATE TABLE ';
						this.estimatedByteLength += 15;
						this.appendTableName(this.tableName);
						break;

					default:
						debugAssert(this.sqlSettings.mode == SqlMode.SQLITE || this.sqlSettings.mode == SqlMode.SQLITE_ONLY);
						this.strings[this.strings.length - 1] += 'DELETE FROM ';
						this.estimatedByteLength += 12;
						this.appendTableName(this.tableName);
				}
				break;
			}
		}
		this.operation = Operation.NONE;
		this.operationSelectColumns = '';
		this.operationSelectOrderBy = '';
		this.operationSelectOffset = 0;
		this.operationSelectLimit = 0;
		this.operationUpdateRow = undefined;
		this.operationInsertRows = undefined;
		this.operationInsertOnConflictDo = '';
		this.operationInsertNames = undefined;
		this.operationInsertSelect = undefined;
	}
}

function wrapRowsIterator(rows: Iterable<Record<string, any>>)
{	let names;
	if (Array.isArray(rows))
	{	if (rows.length == 0)
		{	throw new Error("0 rows in <${param}>");
		}
		names = Object.keys(rows[0]);
	}
	else
	{	let itInner = rows[Symbol.iterator]();
		let {value, done} = itInner.next();
		if (done || !value)
		{	throw new Error("0 rows in <${param}>");
		}
		let firstRow = value;
		names = Object.keys(firstRow);
		function *itOuter()
		{	while (true)
			{	if (firstRow)
				{	yield firstRow;
					firstRow = undefined;
				}
				else
				{	let {value, done} = itInner.next();
					if (done || !value)
					{	break;
					}
					yield value;
				}
			}
		}
		rows = itOuter();
	}
	return {names, rows};
}