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PHP MySQL update supquery

Posted on 2011-02-24
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Last Modified: 2012-05-11
I'm sure this is a pretty simple question, but I can't think of a solution at the moment.  I'm trying to update a decimal value, based on the current value of the field.

I want to reduce the amount in the field by the amount in a variable... something like this...

"currentrequest" is the current field...  So, basically I want to update current request to be it's current value minus 100.00.  

I've tried using a select subquery in there, and it tells me that I can't select the same table...  
The error I receive is: "You can't specify target table 'budget' for update in FROM clause".

Thanks for any shoves in the right direction!


$reqAmt=100.00;

$removeFromBudget=@mysql_query("
   UPDATE budget 
   SET currentrequest='currentrequest-".$reqAmt."' 
   WHERE acct='".$acctNum."' LIMIT 1");

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Question by:cbastian-hill
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Accepted Solution

by:
cbastian-hill earned 0 total points
ID: 34972441
Just found the answer...   Posting in case anyone else needs it...


$removeFromBudget=@mysql_query("
   UPDATE budget 
   SET currentrequest=((SELECT currentrequest)-".$reqAmt.")
   WHERE acct='".$acctNum."' LIMIT 1");

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Expert Comment

by:nanharbison
ID: 34972454
Can you give us the whole query? I don't see a subquery here.
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Author Comment

by:cbastian-hill
ID: 34972473
That is the whole query...  The sub query is in the SET currentrequest..... line...

Are you not seeing that line?  Or am I describing it incorrectly?
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LVL 17

Expert Comment

by:nanharbison
ID: 34972943
That's not a subquery, but glad you found the answer!
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Author Comment

by:cbastian-hill
ID: 34972973
Interesting...  I was always taught that anything like that inside another query would be considered a subquery.  Would you know what it should be called, then?
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LVL 17

Expert Comment

by:nanharbison
ID: 34973097
It just doesn't look like a subquery because UPDATE a table, set something equal to a value is a regular update query, right? But you do have to select a value first before you can change it by doing math on that value...hmm, not sure.Maybe you are right?
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Author Comment

by:cbastian-hill
ID: 34973139
Hmmm....  That is what I was thinking...  The SELECT inside the UPDATE would be a subquery...  I'll have to go back to the books later, when I have some time, and see if I can find an exact definition of what makes a subquery...   Thanks for the info, either way!
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