Index: includes/database/query.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database/query.inc,v
retrieving revision 1.59
diff -u -p -r1.59 query.inc
--- includes/database/query.inc	15 Dec 2010 06:52:54 -0000	1.59
+++ includes/database/query.inc	17 Dec 2010 20:24:07 -0000
@@ -1756,6 +1756,8 @@ class DatabaseCondition implements Query
       'BETWEEN' => array('delimiter' => ' AND '),
       'IN' => array('delimiter' => ', ', 'prefix' => ' (', 'postfix' => ')'),
       'NOT IN' => array('delimiter' => ', ', 'prefix' => ' (', 'postfix' => ')'),
+      'EXISTS' => array('prefix' => ' (', 'postfix' => ')'),
+      'NOT EXISTS' => array('prefix' => ' (', 'postfix' => ')'),
       'IS NULL' => array('use_value' => FALSE),
       'IS NOT NULL' => array('use_value' => FALSE),
       // Use backslash for escaping wildcard characters.
Index: modules/simpletest/tests/database_test.test
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/tests/database_test.test,v
retrieving revision 1.105
diff -u -p -r1.105 database_test.test
--- modules/simpletest/tests/database_test.test	15 Dec 2010 06:52:54 -0000	1.105
+++ modules/simpletest/tests/database_test.test	17 Dec 2010 20:24:19 -0000
@@ -1665,6 +1665,49 @@ class DatabaseSelectSubqueryTestCase ext
 
     $this->assertEqual(count($people), 2, t('Returned the correct number of rows.'));
   }
+
+  /**
+   * Test EXISTS and NOT EXISTS subquery conditionals on SELECT statements.
+   */
+  function testExistsSubquerySelect() {
+    // Put George into {test_people}.
+    db_insert('test_people')
+      ->fields(array(
+        'name' => 'George',
+        'age' => 27,
+        'job' => 'Singer',
+      ))
+      ->execute();
+    // Base query to {test}.
+    $query = db_select('test', 't')
+      ->fields('t', array('name'));
+    // Subquery to {test_people}.
+    $subquery = db_select('test_people', 'tp')
+      ->fields('tp', array('name'))
+      ->condition('name', 'George');
+    $query->condition('', $subquery, 'EXISTS');
+    $result = $query->execute();
+
+    // Ensure that we got the right record.
+    $record = $result->fetch();
+    $this->assertEqual($record->name, 'George', t('Fetched name is correct using EXISTS query.'));
+
+    // Base query to {test}.
+    $query = db_select('test', 't')
+      ->fields('t', array('name'));
+    // Subquery to {test_people}.
+    $subquery = db_select('test_people', 'tp')
+      ->fields('tp', array('name'))
+      ->condition('name', 'George');
+    $query->condition('', $subquery, 'NOT EXISTS');
+    $result = $query->execute();
+
+    // Ensure that we got the right record.
+    $record = $result->fetch();
+    $this->assertFalse($record, t('NOT EXISTS query returned no results.'));
+
+  }
+
 }
 
 /**