Fix incorrect column names for string literals without alias (#296)

It turns out that when selecting a string literal, the resulting column
name differs between MySQL and SQLite.

For example, with a query such as `SELECT 'abc'`:
- In MySQL, the returned column name is `abc` (the unquoted string
value).
- In SQLite, the returned column name is `'abc'` (the quoted string).

To address that, we need to use "SELECT 'abc' AS \`abc\`" in these
cases.

Author: adamziel

tests/WP_SQLite_Driver_Tests.php

@@ -3738,7 +3738,7 @@ public function testHavingWithoutGroupBy() {
 		$this->assertEquals(
 			array(
 				(object) array(
-					"'T'" => 'T',
+					'T' => 'T',
 				),
 			),
 			$result

tests/WP_SQLite_Driver_Translation_Tests.php

@@ -1680,7 +1680,7 @@ public function testSelectOrderByAmbiguousColumnResolution(): void {
 		// Test a complex query with CTEs.
 		$this->assertQuery(
 			'WITH'
-				. " `cte1` ( `name` ) AS ( SELECT 'a' UNION ALL SELECT 'b' ) ,"
+				. " `cte1` ( `name` ) AS ( SELECT 'a' AS `a` UNION ALL SELECT 'b' AS `b` ) ,"
 				. ' `cte2` ( `name` ) AS ( SELECT `t2`.`name` FROM `t2` JOIN `t1` ON `t1`.`id` = `t2`.`id` ORDER BY `t2`.`name` )'
 				. ' SELECT `t1`.`name` , ( SELECT `name` FROM `cte1` WHERE `id` = 1 ) AS `cte1_name` , ( SELECT `name` FROM `cte2` WHERE `id` = 2 ) AS `cte2_name`'
 				. ' FROM `t1`'

wp-includes/sqlite-ast/class-wp-sqlite-driver.php

@@ -4246,6 +4246,22 @@ public function translate_select_item( WP_Parser_Node $node ): string {
 			return $item;
 		}
 
+		/*
+		 * When the select item is a text string literal, we need to use an alias
+		 * to ensure that the column name is the same as it would be in MySQL.
+		 * In MySQL, the column name is the original text string literal value
+		 * without quotes and escaping, but in SQLite, it is the quoted value.
+		 *
+		 * For example, for "SELECT 'abc'", the resulting column name is "abc"
+		 * in MySQL, but would be "'abc'" in SQLite if an alias was not used.
+		 */
+		$text_string_literal    = $node->get_first_descendant_node( 'textStringLiteral' );
+		$is_text_string_literal = $text_string_literal && $item === $this->translate( $text_string_literal );
+		if ( $is_text_string_literal ) {
+			$alias = $text_string_literal->get_first_child_token()->get_value();
+			return sprintf( '%s AS %s', $item, $this->quote_sqlite_identifier( $alias ) );
+		}
+
 		/*
 		 * When the select item has no explicit alias, we need to ensure that the
 		 * returned column name is equivalent to what MySQL infers from the input.