Subquery within scalar subquery fails with error ORA-00936 Missing Expression

1. This is the query that does not work:

   SELECT distinct ord.DateOrdered
      , (SELECT docno 
         FROM th_mm_c_orderline_history 
         WHERE th_mm_c_orderline_history_id 
               in (SELECT max(th_mm_c_orderline_history_id) 
                   FROM th_mm_c_orderline_history 
                   GROUP BY c_orderline_id ) 
         order by docno,c_orderline_id) as docno 
   FROM c_order ord 
   INNER JOIN c_orderline on c_orderline.c_order_id = ord.c_order_id 
   INNER JOIN th_mm_c_orderline_history 
         on th_mm_c_orderline_history.c_order_id=ord.c_order_id
   

   It is throwing me ORA-00936 Missing expression error

2. This query works fine:

   SELECT docno 
   FROM th_mm_c_orderline_history 
   WHERE th_mm_c_orderline_history_id 
         in (SELECT max(th_mm_c_orderline_history_id) 
             FROM th_mm_c_orderline_history 
             GROUP BY c_orderline_id ) 
   order by docno,c_orderline_id as docno
   

Just remove the order by clause from the inline select. You can not use orde by clause there. You can use it in the outer select if you need it...This is how you can do all three of them without the error:

SELECT distinct ord.DateOrdered
       , (SELECT docno FROM th_mm_c_orderline_history 
          WHERE th_mm_c_orderline_history_id 
                 in (SELECT max(th_mm_c_orderline_history_id) 
                     FROM th_mm_c_orderline_history 
                     GROUP BY c_orderline_id) 
          ) as docno 
FROM c_order ord 
INNER JOIN c_orderline on c_orderline.c_order_id = ord.c_order_id 
INNER JOIN th_mm_c_orderline_history on th_mm_c_orderline_history.c_order_id=ord.c_order_id