I would think the one huge query (using an IN clause) would be better than
multiple queries...especially if you structure it to use an index
$query="UPDATE some_table SET x='$y' WHERE id
IN('.$z[$key].','.$z[$another_key].','.$z[$another_key]...
bastien
From: Jeffrey <jeffrey@xxxxxxxxxxx>
To: PHP DB <php-db@xxxxxxxxxxxxx>
Subject: One big query vs. lots of small queries
Date: Mon, 18 Dec 2006 15:23:36 +0100
Here's a question of efficiency.
I have an application in PHP using MySQL.
Users select items on a form and each selected item represents a change in
a table row. It is possible that 100s of changes might be chosen from a
single form.
Which is likely to be faster/more efficient?
multiple queries like...
$query="UPDATE some_table SET x='$y' WHERE id='$z[$key]'";
$result=mysql_query($query);
or one huge query like...
$query="UPDATE some_table SET x='$y' WHERE id='$z[$key]'
OR id='$z[$another_key]' OR id='$z[$another_key]
OR id='$z[$another_key]"; etc?
$result=mysql_query($query);
In the latter, PHP would have to construct the WHERE string, which would
require some processing power as well. Is there a limit to how many OR's
can be added to a mysql query? No - don't answer that, I'll look in the
manual.
Many thanks,
Jeff
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