SQL error / DISTINCT(n.nid) added to certain queries when node access module is enabled

version of MySQL in use?

Actually, I think this is caused by a node access module. Probably, we do not have to use db_rewrite_sql() here.

Could you please try the following changes to subnodes_by_taxonomy.module?

-      $sql = db_rewrite_sql('SELECT n.vid, n.nid, '. $content_taxonomy_column .' AS tid
+      $sql = 'SELECT n.vid, n.nid, '. $content_taxonomy_column .' AS tid
         FROM {node} n
           INNER JOIN {'. $nodereference_table .'} nr ON nr.vid = n.vid AND nr.nid = n.nid
           '. $content_taxonomy_join .'
-        WHERE nr.'. $nodereference_column .' = %d', 'n', 'vid');
+        WHERE nr.'. $nodereference_column .' = %d';

-      $sql = db_rewrite_sql('SELECT nr.'. $nodereference_column .' AS nid, '. $content_taxonomy_column .' AS tid
+      $sql = 'SELECT nr.'. $nodereference_column .' AS nid, '. $content_taxonomy_column .' AS tid
         FROM {node} n
           INNER JOIN {'. $nodereference_table .'} nr ON nr.vid = n.vid AND nr.nid = n.nid
           '. $content_taxonomy_join .'
-        WHERE n.nid = %d');
+        WHERE n.nid = %d';

Well, I have committed the fix in #2 to CVS.

Re: "thank you for sharing your work, hope you benefit from people joining into some testing."

Sure, thanks for reporting this issue. Also, if it doesn't exactly fit into someone else's use-case, maybe it can be used as an example on how to play with CCK fields and relations between nodes.

Our use case is: parent nodes are Games, and child nodes are Platforms. Each game can be related to one or more platforms, and there are a lot of attributes that need to be managed at Game/Platform level, hence we use child nodes, and the platforms are taxonomies that give meaning to the relation. Game/Platform data can be edited from the tabs in the parent game node. We also had to write a module that allows us to enable/disable Game/Platform fields depending on the platform, but that one has a lot of particular customizations and it cannot be shared. The whole thing works like a charm.

Please, open a separate support request.