feat: add DEFAULT helper support for SQLite

- Add testDefaultHelper() test for SQLite to match other dialects
- Handle DEFAULT keyword in RawValueResolver for SQLite (replace with NULL)
- Update buildRawValueExpression() in SqliteDialect to handle DEFAULT in UPSERT operations
- SQLite doesn't support DEFAULT in UPDATE, so we use NULL as equivalent

Author: tommyknocker

src/dialects/SqliteDialect.php

@@ -319,7 +319,13 @@ protected function buildIncrementExpression(string $colSql, array $expr, string
      */
     protected function buildRawValueExpression(string $colSql, RawValue $expr, string $tableName, string $col): string
     {
-        return "{$colSql} = {$expr->getValue()}";
+        // SQLite doesn't support DEFAULT keyword in UPDATE statements
+        // Replace DEFAULT with NULL (closest equivalent behavior)
+        $value = $expr->getValue();
+        if (trim($value) === 'DEFAULT') {
+            return "{$colSql} = NULL";
+        }
+        return "{$colSql} = {$value}";
     }
 
     /**

src/query/RawValueResolver.php

@@ -6,6 +6,7 @@
 
 use tommyknocker\pdodb\connection\ConnectionInterface;
 use tommyknocker\pdodb\dialects\DialectInterface;
+use tommyknocker\pdodb\dialects\SqliteDialect;
 use tommyknocker\pdodb\helpers\values\ConcatValue;
 use tommyknocker\pdodb\helpers\values\ConfigValue;
 use tommyknocker\pdodb\helpers\values\CurDateValue;
@@ -186,6 +187,12 @@ public function resolveRawValue(string|RawValue $value): string
         $sql = $value->getValue();
         $params = $value->getParams();
 
+        // SQLite doesn't support DEFAULT keyword in UPDATE statements
+        // Replace DEFAULT with NULL (closest equivalent behavior)
+        if (trim($sql) === 'DEFAULT' && $this->dialect instanceof SqliteDialect) {
+            return 'NULL';
+        }
+
         if (empty($params)) {
             return $sql;
         }

tests/sqlite/HelpersTests.php

@@ -130,6 +130,30 @@ public function testIsNullIsNotNullHelpers(): void
         $this->assertEquals('Helen', $notNullResults[0]['name']);
     }
 
+    public function testDefaultHelper(): void
+    {
+        $db = self::$db;
+
+        $userId = $db->find()->table('users')->insert([
+        'name' => 'Nina',
+        'company' => 'DefaultCorp',
+        'age' => 31,
+        'status' => 'active',
+        ]);
+
+        $db->find()
+        ->table('users')
+        ->where('id', $userId)
+        ->update(['status' => Db::default()]);
+
+        $result = $db->find()
+        ->from('users')
+        ->where('id', $userId)
+        ->getOne();
+
+        $this->assertNull($result['status']);
+    }
+
     public function testCaseInSelect(): void
     {
         $db = self::$db;