mysql> explain select nid as nid2, node as node2 from tig_nodes, (select nid as nid1 from tig_nodes where (uid = 18033992) AND (parent_nid is null) AND (node = 'root')) nodes1 where (parent_nid = nid1) AND (node = 'message-archive') \G

*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: tig_nodes
   partitions: NULL
         type: ref
possible_keys: PRIMARY,tnode,node,uid,parent_nid
          key: tnode
      key_len: 784
          ref: const,const,const
         rows: 1
     filtered: 100.00
        Extra: Using where; Using index
*************************** 2. row ***************************
           id: 1
  select_type: SIMPLE
        table: tig_nodes
   partitions: NULL
         type: ref
possible_keys: tnode,node,parent_nid
          key: node
      key_len: 767
          ref: const
         rows: 149706
     filtered: 100.00
        Extra: Using where
2 rows in set, 1 warning (0.00 sec)