Topic: SQL*Plus and PL/SQL >> Usage of "where exists" clause
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| Title: Usage of "where exists" clause |
| Nash |
Posted: Aug 30, 2008 11:45:21 PM |
Total Post: 1
Joined: Aug, 2008
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Consider tables A and B. Both the tables have columns x,y and z. Column x of A is updated with column x of B based on the equality condition, A.y=B.y and A.z= B.z.
May I know the difference between the update statements given below?
i) update B
set x=( Select x
from A
where A.y=B.y
and A.z=B.z)
ii) update B
set x=( Select x
from A
where A.y=B.y
and A.z=B.z)
where exists(Select y,z
from A
where A.y=B.y
and A.z=B.z) |
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 6s |
| Posted: Sep 01, 2008 04:34:24 AM |  |
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Total Post: 1
Joined: Sep, 2008
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If the subquery returns at least one row, then only the entire update will work (atleast updation of one row will happen).
So whenever EXISTS is used and your DML task is done, be sure the subquery condition has been met.
You can use NOT EXISTS as well.
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