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Fix ROLLBACK as the first transaction of a connection #535

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Nandan108 wants to merge 1 commit into from
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Fix ROLLBACK as the first transaction of a connection #535

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47 changes: 34 additions & 13 deletions packages/mysql-on-sqlite/src/sqlite/class-wp-mysql-on-sqlite.php
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Original file line number Diff line number Diff line change
Expand Up @@ -7747,21 +7747,28 @@ private function create_result_statement_from_data( array $columns, array $rows
* lock. Writing to a connection-private TEMP table uses the temp
* database, which has no shared lock, so it never contends.
*/
$empty_insert = sprintf(
'INSERT INTO %s ( placeholder_for_empty_insert ) SELECT NULL WHERE FALSE',
$this->quote_sqlite_identifier( self::EMPTY_RESULT_TABLE_NAME )
);
if ( ! $this->empty_result_table_ready ) {
$pdo->exec(
sprintf(
'CREATE TEMP TABLE IF NOT EXISTS %s ( placeholder_for_empty_insert )',
$this->quote_sqlite_identifier( self::EMPTY_RESULT_TABLE_NAME )
)
);

@JanJakes JanJakes Oct 15, 2026

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Oh, this is becoming kind of complex. I guess we could just always do:

CREATE TEMP TABLE IF NOT EXISTS %s ( placeholder_for_empty_insert );
INSERT INTO %s ( placeholder_for_empty_insert ) SELECT NULL WHERE FALSE;

Or maybe there's a way to make an empty statement without any queries. Checking 馃憖

@JanJakes JanJakes Oct 16, 2026

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There is, implemented in #537.

$this->empty_result_table_ready = true;
$this->create_empty_result_table();
}
try {
return $pdo->query( $empty_insert );
} catch ( PDOException $e ) {
/*
* Even though we keep track of whether the table was already
* created, the tracked information may be incorrect when the
* table was created in a transaction that was later rolled back.
* In that case, let's create the table again, and try again.
*/
if ( ! str_contains( $e->getMessage(), 'no such table' ) ) {
throw $e;
}
$this->create_empty_result_table();
return $pdo->query( $empty_insert );
}
return $pdo->query(
sprintf(
'INSERT INTO %s ( placeholder_for_empty_insert ) SELECT NULL WHERE FALSE',
$this->quote_sqlite_identifier( self::EMPTY_RESULT_TABLE_NAME )
)
);
}

/*
Expand Down Expand Up @@ -7815,6 +7822,20 @@ private function create_result_statement_from_data( array $columns, array $rows
return $pdo->query( $query );
}

/**
* Create the TEMP table backing empty result sets on this connection.
* See create_result_statement_from_data().
*/
private function create_empty_result_table(): void {
$this->connection->get_pdo()->exec(
sprintf(
'CREATE TEMP TABLE IF NOT EXISTS %s ( placeholder_for_empty_insert )',
$this->quote_sqlite_identifier( self::EMPTY_RESULT_TABLE_NAME )
)
);
$this->empty_result_table_ready = true;
}

/**
* Create a new MySQL-on-SQLite driver exception.
*
Expand Down
23 changes: 23 additions & 0 deletions packages/mysql-on-sqlite/tests/WP_MySQL_On_SQLite_PDO_API_Tests.php
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Original file line number Diff line number Diff line change
Expand Up @@ -888,6 +888,29 @@ public function test_rollback(): void {
$this->assertTrue( $result );
}

public function test_rollback_statement_as_first_transaction_on_connection(): void {
// The first empty result set on the connection is created in the transaction.
$this->driver->exec( 'START TRANSACTION' );
$this->driver->exec( 'ROLLBACK' );
$this->assertFalse( $this->driver->inTransaction() );

// Statements with empty result sets keep working after the rollback.
$this->driver->exec( 'START TRANSACTION' );
$this->driver->exec( 'CREATE TABLE t (id INT)' );
$this->driver->exec( 'ROLLBACK' );
$this->assertSame( 0, $this->driver->exec( 'CREATE TABLE t (id INT)' ) );
}

public function test_rollback_method_as_first_transaction_on_connection(): void {
// The first empty result set on the connection is created in the transaction.
$this->driver->beginTransaction();
$this->driver->exec( 'CREATE TABLE t (id INT)' );
$this->assertTrue( $this->driver->rollBack() );

// Statements with empty result sets keep working after the rollback.
$this->assertSame( 0, $this->driver->exec( 'CREATE TABLE t (id INT)' ) );
}

public function test_rollback_no_active_transaction(): void {
$this->expectException( PDOException::class );
$this->expectExceptionMessage( 'There is no active transaction' );
Expand Down
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