Index: includes/database/query.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database/query.inc,v
retrieving revision 1.5
diff -u -p -r1.5 query.inc
--- includes/database/query.inc	6 Oct 2008 14:39:40 -0000	1.5
+++ includes/database/query.inc	8 Nov 2008 06:35:08 -0000
@@ -1032,7 +1032,7 @@ class DatabaseCondition implements Query
           if ($condition['field'] instanceof QueryConditionInterface) {
             // Compile the sub-condition recursively and add it to the list.
             $condition['field']->compile($connection);
-            $condition_fragments[] = (string)$condition['field'];
+            $condition_fragments[] = '(' . (string)$condition['field'] . ')';
             $arguments += $condition['field']->arguments();
           }
           else {
Index: modules/simpletest/tests/database_test.test
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/tests/database_test.test,v
retrieving revision 1.13
diff -u -p -r1.13 database_test.test
--- modules/simpletest/tests/database_test.test	25 Oct 2008 04:26:30 -0000	1.13
+++ modules/simpletest/tests/database_test.test	8 Nov 2008 06:35:08 -0000
@@ -1416,6 +1416,23 @@ class DatabaseSelectComplexTestCase exte
       $this->assertTrue(FALSE, $e->getMessage());
     }
   }
+
+  /**
+   * Confirm that we can properly nest conditional clauses.
+   */
+  function testNestedConditions() {
+    // This query should translate to:
+    // "SELECT job FROM {test} WHERE name="Paul" AND (age=26 OR age=27)"
+    // That should find only one record.  Yes it's a non-optimal way of writing
+    // that query but that's not the point!
+    $query = db_select('test');
+    $query->addField('test', 'job');
+    $query->condition('name', 'Paul');
+    $query->condition(db_or()->condition('age', 26)->condition('age', 27));
+
+    $job = $query->execute()->fetchField();
+    $this->assertEqual($job, 'Songwriter', t('Correct data retrieved.'));
+  }
 }
 
 /**