=== modified file 'includes/database/select.inc'
--- includes/database/select.inc	2009-08-29 05:43:34 +0000
+++ includes/database/select.inc	2009-08-31 09:05:23 +0000
@@ -112,6 +112,24 @@ interface SelectQueryInterface extends Q
   public function &getTables();
 
   /**
+   * Returns a reference to the union queries for this query.
+   *
+   * Because this method returns by reference, alter hooks may edit the tables
+   * array directly to make their changes. If just adding union queries,
+   * however, the use of the union() method is preferred.
+   *
+   * Note that this method must be called by reference as well:
+   *
+   * @code
+   * $fields =& $query->getUnion();
+   * @endcode
+   *
+   * @return
+   *   A reference to the union query array structure.
+   */
+  public function &getUnion();
+
+  /**
    * Compiles and returns an associative array of the arguments for this prepared statement.
    *
    * @param $queryPlaceholder
@@ -345,6 +363,27 @@ interface SelectQueryInterface extends Q
   public function range($start = NULL, $length = NULL);
 
   /**
+   * Add another Select query to UNION to this one.
+   *
+   * Union queries consist of two or more queries whose
+   * results are effectively concatenated together. Queries
+   * will be UNIONed in the order they are specified, with
+   * this object's query coming first.
+   *
+   * Note: All queries UNIONed together must have the same
+   * field structure, in the same order. It is up to the
+   * caller to ensure that they match properly. If they do
+   * not, an SQL syntax error will result.
+   *
+   * @param $query
+   *   The query to UNION to this query.
+   * @return
+   *   The called object.
+   */
+  public function union(SelectQueryInterface $query);
+
+
+  /**
    * Groups the result set by the specified field.
    *
    * @param $field
@@ -524,6 +563,10 @@ class SelectQueryExtender implements Sel
     return $this->query->getTables();
   }
 
+  public function &getUnion() {
+    return $this->query->getUnion();
+  }
+
   public function getArguments(QueryPlaceholderInterface $queryPlaceholder = NULL) {
     return $this->query->getArguments($queryPlaceholder);
   }
@@ -600,6 +643,11 @@ class SelectQueryExtender implements Sel
     return $this;
   }
 
+  public function union(SelectQueryInterface $query) {
+    $this->query->union($query);
+    return $this;
+  }
+
   public function groupBy($field) {
     $this->query->groupBy($field);
     return $this;
@@ -766,6 +814,16 @@ class SelectQuery extends Query implemen
   protected $range;
 
   /**
+   * An array of additional Select queries.
+   *
+   * If populated, all queries in this array
+   * and this query will be UNIONed together.
+   *
+   * @var array
+   */
+  protected $union = array();
+
+  /**
    * Indicates if preExecute() has already been called.
    * @var boolean
    */
@@ -910,6 +968,10 @@ class SelectQuery extends Query implemen
     return $this->tables;
   }
 
+  public function &getUnion() {
+  	return $this->union;
+  }
+
   public function getArguments(QueryPlaceholderInterface $queryPlaceholder = NULL) {
     if (!isset($queryPlaceholder)) {
       $queryPlaceholder = $this;
@@ -917,6 +979,7 @@ class SelectQuery extends Query implemen
     $this->where->compile($this->connection, $queryPlaceholder);
     $this->having->compile($this->connection, $queryPlaceholder);
     $args = $this->where->arguments() + $this->having->arguments();
+
     foreach ($this->tables as $table) {
       if ($table['arguments']) {
         $args += $table['arguments'];
@@ -926,12 +989,19 @@ class SelectQuery extends Query implemen
         $args += $table['table']->getArguments($queryPlaceholder);
       }
     }
+
     foreach ($this->expressions as $expression) {
       if ($expression['arguments']) {
         $args += $expression['arguments'];
       }
     }
 
+    // If there are any dependent queries to UNION,
+    // incorporate their arguments recursively.
+    foreach ($this->union as $union) {
+      $args += $union->getArguments($queryPlaceholder);
+    }
+
     return $args;
   }
 
@@ -1109,6 +1179,11 @@ class SelectQuery extends Query implemen
     return $this;
   }
 
+  public function union(SelectQueryInterface $query) {
+  	$this->union[] = $query;
+  	return $this;
+  }
+
   public function groupBy($field) {
     $this->group[] = $field;
     return $this;
@@ -1223,16 +1298,31 @@ class SelectQuery extends Query implemen
     }
 
     // RANGE is database specific, so we can't do it here.
+
+    // UNION is a little odd, as the select queries to
+    // combine are passed into this query but syntactically
+    // they all end up on the same level.
+    if ($this->union) {
+	    $unions[] = $query;
+	    foreach ($this->union as $union) {
+	      $unions[] = (string)$union;
+	    }
+	    $query = implode(' UNION ', $unions);
+    }
+
     return $query;
   }
 
   public function __clone() {
-    // On cloning, also clone the conditional objects. However, we do not
+    // On cloning, also clone the dependent objects. However, we do not
     // want to clone the database connection object as that would duplicate the
     // connection itself.
 
     $this->where = clone($this->where);
     $this->having = clone($this->having);
+    foreach ($this->union as $key => $query) {
+      $this->union[$key] = clone($query);
+    }
   }
 }
 

=== modified file 'modules/simpletest/tests/database_test.test'
--- modules/simpletest/tests/database_test.test	2009-08-22 19:43:11 +0000
+++ modules/simpletest/tests/database_test.test	2009-08-31 09:01:45 +0000
@@ -1352,6 +1352,26 @@ class DatabaseSelectTestCase extends Dat
     $this->assertEqual($names[0], 'Gonzo', t('Correct record returned for NOT NULL age.'));
     $this->assertEqual($names[1], 'Kermit', t('Correct record returned for NOT NULL age.'));
   }
+
+  /**
+   * Test that we can UNION multiple Select queries together.
+   */
+  function testUnion() {
+    $query_1 = db_select('test', 't')
+      ->fields('t', array('name'))
+      ->condition('age', 27);
+
+    $query_2 = db_select('test', 't')
+      ->fields('t', array('name'))
+      ->condition('age', 28);
+
+    $query_1->union($query_2);
+
+    $names = $query_1->execute()->fetchCol();
+
+    $this->assertEqual($names[0], 'George', t('First query returned correct name.'));
+    $this->assertEqual($names[1], 'Ringo', t('Second query returned correct name.'));
+  }
 }
 
 /**