Message-ID: <47D803E0.5050207@encs.concordia.ca>
Date: Wed, 12 Mar 2008 12:25:04 -0400
From: Emi Lu <emilu@encs.concordia.ca>
Reply-To: emilu@encs.concordia.ca
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To: Scott Marlowe <scott.marlowe@gmail.com>
CC: pgsql-sql@postgresql.org
Subject: Re: case when... end in update clause?
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	<dcc563d10803120919w5d26ff5amb7c0cf10cfcb99df@mail.gmail.com>
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Hi Scott ,
>>  No. I provide one small fake example.
>>
>>
>>  I want to know how to use case when in update/set clause as the following:
>>
>>  update test
>>  set id = case when id = 5 then 6 else id end;
> 
> Well, I think my point stands, that this stuff really belongs in a
> where clause.  The way you're doing it it updates ALL the rows whether
> it needs to or not, my way only updates the rows that need it.  How
> about a REAL example of what you're trying to do.  There may well be a
> more efficient way of doing this than using a case statement.  Or
> not...

Ok.


The situation would like this, in one query:


UPDATE tableName
SET
    col1 = val1 when col1 satisfy condition1
    col1 = val2 when col1 satisfy condition2

    ... ...

    col1 = valN when col1 satisfy conditionN

    ... ...

WHERE
    col3 satisfy conditionX;