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update SQL with sub-query

 
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tzeche

New User


Joined: 08 Jun 2007
Posts: 3
Location: Philippines

PostPosted: Wed Mar 04, 2015 1:30 pm    Post subject: update SQL with sub-query
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I have an update query below and need to convert it to test first whether the sub-query (SELECT MAX(COL_A) FROM TABLE2 WHERE COL_B = TB1.COL_2) returns a NULL value

UPDATE TABLE1 TB1
SET COL_1 = (SELECT MAX(COL_A) FROM TABLE2
WHERE COL_B = TB1.COL_2)


If the sub-query returns a NULL then COL_1 will retain it's existing value but if not then COL_1 will be updated with the value returned from the sub-query

Please help me, I can't seem to get it right.

Do I need to use CASE? How?
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GuyC

Senior Member


Joined: 11 Aug 2009
Posts: 1281
Location: Belgium

PostPosted: Wed Mar 04, 2015 5:14 pm    Post subject:
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untested:
Quote:
UPDATE TABLE1 TB1
SET COL_1 = (SELECT MAX(COL_A) FROM TABLE2
WHERE COL_B = TB1.COL_2)
where exists(SELECT COL_A FROM TABLE2
WHERE COL_B = TB1.COL_2 and col_A is not null)
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tzeche

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Joined: 08 Jun 2007
Posts: 3
Location: Philippines

PostPosted: Thu Mar 05, 2015 11:04 pm    Post subject:
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Thank you GuyC! it worked fine!
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