Re: Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in

[Dan Makovec]

To clarify, the reason I suspect a possible linkage is as follows:

In the bug I described, occasionally MySQL (4.1.11 at least, never seen it in 4.0.x) returns a "SELECT/INSERT/UPDATE/DELETE command denied" error to a perfectly valid query from a user with all the correct permissions. If you run the identical query again it probably runs fine.

Hence if, say for example in PHP, you have the following code...

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$resultset = mysql_query("SELECT ...", $conn_id);

$rows= mysql_num_rows($resultset)
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...and you're not checking that $resultset is valid, you'll get the warning described above.

To test this hypothesis, try changing the code to the following:
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$resultset = mysql_query("SELECT ...", $conn_id);

if (!isset($resultset))
$rows= mysql_num_rows($resultset)
else
print "Error from MySQL: ".mysql_error($conn_id)."\n";

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If the error turns out to be a permissions problem, but re-running the code works perfectly, post to some feedback to http://bugs.mysql.com/bug.php?id=11958