Use of Select stmts with Update stmts

Question

Hi,
I want to execute the following update stmt...
UPDATE Test1_tab a
SET a.invpln_seq_no = (SELECT b.seq_no
FROM Test2_tab b
WHERE b.contract_id = a.contract_id
AND b.date_from = a.period_from_date)
WHERE a.invpln_seq_no != (SELECT b.seq_no
FROM Test2_tab b
WHERE b.contract_id = a.contract_id
AND b.date_from = a.period_from_date)
Here the problem is I have used 'SELECT b.seq_no FROM Test2_tab b WHERE b.contract_id = a.contract_id AND b.date_from = a.period_from_date' twice, one in the SET clause and the other one in WHERE clause...But it is the same SELECT stmt...So this same Select stmt runs twice when I run the whole update stmt I guess. Is there a way to do the above update, where it runs the SELECT stmt only once...
Any input is highly appreciated...
Thanks And Best Regards,
/Dinesh...

Answer 1

Then you can use Merge statement instead.
try this
merge into test1_tab t1
using
(SELECT a.rowid,b.seq_no SEQ_DEST
FROM test1_tab a,test2_tab b
WHERE b.contract_id = a.contract_id
AND  b.date_from = a.period_from_date
AND a.invpln_seq_no != b.seq_no) t2
ON (t1.rowid=t2.rowid)
WHEN MATCHED THEN
UPDATE SET t1.invpln_seq_no=t2.seq_destor if you are sure that sno is a unique key with out any duplicates and if you are going to perform one time manual update then you can use an undocumented hint /*+ bypass_ujvc */ to do this.
*DO NOT include this code if you are about to add it in a production procedure or a function
UPDATE /*+ bypass_ujvc */ (SELECT a.invpln_seq_no SEQ_SRC,b.seq_no SEQ_DEST FROM test1_tab a,test2_tab  b
WHERE b.contract_id = a.contract_id
AND  b.date_from = a.period_from_date
AND a.invpln_seq_no != b.seq_no)
SET SEQ_SRC = SEQ_DESTRegards,
Prazy