Index: includes/database.pgsql.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database.pgsql.inc,v
retrieving revision 1.68.2.1
diff -u -r1.68.2.1 database.pgsql.inc
--- includes/database.pgsql.inc	7 Feb 2008 10:17:26 -0000	1.68.2.1
+++ includes/database.pgsql.inc	8 Mar 2008 13:17:22 -0000
@@ -418,11 +418,15 @@
  * @return SQL query with the DISTINCT wrapper surrounding the given table.field.
  */
 function db_distinct_field($table, $field, $query) {
-  $field_to_select = 'DISTINCT ON ('. $table .'.'. $field .") $table.$field";
-  // (?<!text) is a negative look-behind (no need to rewrite queries that already use DISTINCT).
-  $query = preg_replace('/(SELECT.*)(?:'. $table .'\.|\s)(?<!DISTINCT\()(?<!DISTINCT\('. $table .'\.)'. $field .'(.*FROM )/AUsi', '\1 '. $field_to_select .'\2', $query);
-  $query = preg_replace('/(ORDER BY )(?!'. $table .'\.'. $field .')/', '\1'."$table.$field, ", $query);
-  return $query;
+    if (!preg_match('/FROM\s+\S+\s+AS/si', $query)
+      && !preg_match('/DISTINCT\s+ON\s*\(\s*('. $table .'\s*\.\s*)?'. $field .'\s*\)/si', $query)
+      && !preg_match('/DISTINCT[ (]'. $field .'/si', $query)
+      && preg_match('/(.*FROM\s+)(.*?\s)(\s*(WHERE|GROUP|HAVING|ORDER|LIMIT|FOR).*)/Asi', $query, $m)) {
+        $query = $m[1];
+        $query .= preg_replace('/([\{\w+\}]+)\s+(' . $table . ')\s/Usi', '(SELECT DISTINCT ON (' . $field . ') * FROM \1) \2 ', $m[2]);
+        $query .= $m[3];
+    }
+    return $query;
 }
 
 /**