Subquery in update not seeing parent value

Question

Hi all,
I'm working on a complex update statement that I will try to state as simply as possible.
update table1 x set value1=(select value1 from table1
                                        where acct_num=x.acct_num
                                        and trans_dt=(select max(trans_dt) from table1 where acct_num=x.acct_num and [many more conditions])
                                        [and many more conditions]All of this is working fine. Where I reach the problem is when I need to add a condition to verify a field is not the same as the previous field in the table (if one exists), so I try this code I found online (and it works fine when I try it with test data)...
AND vend_id <>  NVL((SELECT vend_id FROM (SELECT c.*, ROWNUM rnum FROM (SELECT * FROM table1
                                                              WHERE acct_num=x.acct_num
                                                  AND trans_dt<x.trans_dt
                                                        ORDER BY trans_dt DESC) c
                                                     WHERE ROWNUM<=2)
                                      WHERE rnum>=2)
                        ,'XXX')but when I try to run it in the update query, I get an error, "x.trans_dt" invalid identifier. This is just another condition to what was posted in the first code block and Oracle "sees" all the x.* values there fine.
Can anyone tell me what is wrong here and how I can pass these values into this condition?
Thanks!

Answer 1

<tt>x.trans_dt</tt> and <tt>x.trans_dt</tt> are just nested too deeply (can only be on next level)
AND vend_id <> NVL((SELECT vend_id
                      FROM (SELECT c.*, ROWNUM rnum
                              FROM (SELECT *
                                      FROM table1
                            WHERE acct_num = x.acct_num
                              AND trans_dt < x.trans_dt
                            ORDER BY trans_dt DESC
                                   ) c
                    WHERE ROWNUM <= 2
                     WHERE rnum >= 2
                   'XXX'
                  )use <tt>merge</tt> to do the update
Regards
Etbin