| Basic Update question [message #23520] |
Sat, 14 December 2002 08:13  |
Reddy Peram
Messages: 52
Registered: December 2002
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Member |
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UPDATE tableA A set (col1,col2,...col10) = (SELECT col1,col2,col3..col10 FROM tableB B
WHERE B.KEY1 = A.KEY1
AND B.Key2 = A.Key2);
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UPDATE tableA A set (col1,col2,...col10) = (SELECT col1,col2,col3..col10 FROM tableB B
WHERE B.KEY1 = A.KEY1
AND B.Key2 = A.Key2)
where exists
SELECT null FROM tableB B
WHERE B.KEY1 = A.KEY1
AND B.Key2 = A.Key2;
Are both these update statements same?
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| Re: Basic Update question [message #23531 is a reply to message #23520] |
Sun, 15 December 2002 16:07  |
Todd Barry
Messages: 4819
Registered: August 2001
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Senior Member |
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No, they are not.
Statement #1 will update every row in tableA regardless of whether a matching row in found in tableB. Rows with no match will have the listed columns updated to a NULL value.
Statement #2 will only update the rows that have a matching row in tableB.
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