Add support for DATE_ADD and DATE_SUB functions

Author: JanJakes

tests/WP_SQLite_Driver_Tests.php

@@ -506,6 +506,94 @@ public function testSelectIndexHintUseGroup() {
 		$this->assertEquals( 1, $result[0]->output );
 	}
 
+    public function testDateAddFunction() {
+        // second
+        $result = $this->assertQuery(
+            'SELECT DATE_ADD("2008-01-02 13:29:17", INTERVAL 1 SECOND) as output'
+        );
+        $this->assertEquals( '2008-01-02 13:29:18', $result[0]->output );
+
+        // minute
+        $result = $this->assertQuery(
+            'SELECT DATE_ADD("2008-01-02 13:29:17", INTERVAL 1 MINUTE) as output'
+        );
+        $this->assertEquals( '2008-01-02 13:30:17', $result[0]->output );
+
+        // hour
+        $result = $this->assertQuery(
+            'SELECT DATE_ADD("2008-01-02 13:29:17", INTERVAL 1 HOUR) as output'
+        );
+        $this->assertEquals( '2008-01-02 14:29:17', $result[0]->output );
+
+        // day
+        $result = $this->assertQuery(
+            'SELECT DATE_ADD("2008-01-02 13:29:17", INTERVAL 1 DAY) as output'
+        );
+        $this->assertEquals( '2008-01-03 13:29:17', $result[0]->output );
+
+        // week
+        $result = $this->assertQuery(
+            'SELECT DATE_ADD("2008-01-02 13:29:17", INTERVAL 1 WEEK) as output'
+        );
+        $this->assertEquals( '2008-01-09 13:29:17', $result[0]->output );
+
+        // month
+        $result = $this->assertQuery(
+            'SELECT DATE_ADD("2008-01-02 13:29:17", INTERVAL 1 MONTH) as output'
+        );
+        $this->assertEquals( '2008-02-02 13:29:17', $result[0]->output );
+
+        // year
+        $result = $this->assertQuery(
+            'SELECT DATE_ADD("2008-01-02 13:29:17", INTERVAL 1 YEAR) as output'
+        );
+        $this->assertEquals( '2009-01-02 13:29:17', $result[0]->output );
+    }
+
+    public function testDateSubFunction() {
+        // second
+        $result = $this->assertQuery(
+            'SELECT DATE_SUB("2008-01-02 13:29:17", INTERVAL 1 SECOND) as output'
+        );
+        $this->assertEquals( '2008-01-02 13:29:16', $result[0]->output );
+
+        // minute
+        $result = $this->assertQuery(
+            'SELECT DATE_SUB("2008-01-02 13:29:17", INTERVAL 1 MINUTE) as output'
+        );
+        $this->assertEquals( '2008-01-02 13:28:17', $result[0]->output );
+
+        // hour
+        $result = $this->assertQuery(
+            'SELECT DATE_SUB("2008-01-02 13:29:17", INTERVAL 1 HOUR) as output'
+        );
+        $this->assertEquals( '2008-01-02 12:29:17', $result[0]->output );
+
+        // day
+        $result = $this->assertQuery(
+            'SELECT DATE_SUB("2008-01-02 13:29:17", INTERVAL 1 DAY) as output'
+        );
+        $this->assertEquals( '2008-01-01 13:29:17', $result[0]->output );
+
+        // week
+        $result = $this->assertQuery(
+            'SELECT DATE_SUB("2008-01-02 13:29:17", INTERVAL 1 WEEK) as output'
+        );
+        $this->assertEquals( '2007-12-26 13:29:17', $result[0]->output );
+
+        // month
+        $result = $this->assertQuery(
+            'SELECT DATE_SUB("2008-01-02 13:29:17", INTERVAL 1 MONTH) as output'
+        );
+        $this->assertEquals( '2007-12-02 13:29:17', $result[0]->output );
+
+        // year
+        $result = $this->assertQuery(
+            'SELECT DATE_SUB("2008-01-02 13:29:17", INTERVAL 1 YEAR) as output'
+        );
+        $this->assertEquals( '2007-01-02 13:29:17', $result[0]->output );
+    }
+
 	public function testLeftFunction1Char() {
 		$result = $this->assertQuery(
 			'SELECT LEFT("abc", 1) as output'

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

@@ -1450,6 +1450,22 @@ private function translate_runtime_function_call( WP_Parser_Node $node ): string
         }
 
         switch ( $child->id ) {
+            case WP_MySQL_Lexer::DATE_ADD_SYMBOL:
+            case WP_MySQL_Lexer::DATE_SUB_SYMBOL:
+                $nodes = $node->get_child_nodes();
+                $value = $this->translate( $nodes[1] );
+                $unit  = $this->translate( $nodes[2] );
+                if ( 'WEEK' === $unit ) {
+                    $unit = 'DAY';
+                    $value = 7 * $value;
+                }
+                return sprintf(
+                    "DATETIME(%s, '%s%s %s')",
+                    $this->translate( $nodes[0] ),
+                    WP_MySQL_Lexer::DATE_SUB_SYMBOL === $child->id ? '-' : '+',
+                    $value,
+                    $unit
+                );
             case WP_MySQL_Lexer::LEFT_SYMBOL:
                 $nodes = $node->get_child_nodes();
                 return sprintf(