Index: views_query.inc
===================================================================
RCS file: /cvs/drupal/contributions/modules/views/views_query.inc,v
retrieving revision 1.59
diff -u -r1.59 views_query.inc
--- views_query.inc     3 Dec 2006 17:28:17 -0000       1.59
+++ views_query.inc     11 Dec 2006 22:25:49 -0000
@@ -310,9 +310,18 @@
     if ($alias) {
       $a = " AS $this->use_alias_prefix$alias";
     }
-    if (!in_array("$table$field$a", $this->fields)) {
-      $this->fields[] = "$table$field$a";
+    foreach ($this->fields as $k => $f) {
+      if (preg_match("/((DISTINCT)[(])?{$table}{$field}([)])?({$a})?/", $f, $matches)) {
+        if (isset($matches[4]) && $matches[4] != $a) {
+          drupal_set_message(t('%field is already in fields list with a different alias', array('%field' => "$table$field")), 'error');
+        }
+        else {
+          $this->fields[$k] = "{$matches[1]}$table$field{$matches[3]}$a";
+        }
+        return;
+      }
     }
+    $this->fields[] = "$table$field$a";
   }
 
   /*