mssql_num_rows error, but query works - php

Question

Hi I am writing to a remote MSSQL 2005 server from a php application, and have a situation where mssql_num_rows errors out with the "mssql_num_rows() expects parameter 1 to be resource, boolean given" message.... but I can't figure out why
$writeitem = "INSERT INTO RebateSubmissionProducts VALUES ('" . $buyproduct . "'," . $quantity . ",CAST('" . $itemUUID . "' as UNIQUEIDENTIFIER),CAST('" . $eligible . "' as UNIQUEIDENTIFIER),CAST('" . $prodID . "' as UNIQUEIDENTIFIER),CAST('" . $UUID . "' as UNIQUEIDENTIFIER),NULL)";
$itemresult = mssql_query($writeitem);
if (!mssql_num_rows($itemresult)){
echo 'Problem writing to RebateSubmissionProducts';
} else {
echo 'Success writing to RebateSubmissionProducts';
}
mssql_free_result($itemresult);
The upshot is that I get the error message, but the insert works fine.
BTW all the input is run through HTMLPurifier so don't slag me too hard about that. The hosting company can't set up PDO_DBLIB so I can't use PDO/bound params.... I also don't have access to the MS server for creating a stored procedure.
Any ideas why php thinks that $itemresult is a boolean? (both mssql_num_rows and mssql_free_result issue the same error message)

Answer 1

As andrewsi pointed out, mssql_num_rows() responds in a different way depending on the query. In my case, I was running an insert, and so when this ran:
$itemresult = mssql_query($writeitem);
$itemresult was boolean(TRUE) beacuse the insert succeeded, so mssql_num_rows (and mssql_free_result() both issued warnings since there wasn't a result set.