[TYPO3-dev] Problem with sql query

[Brian Bendtsen]

Hi

First of all I have this select statement in an extension I have developed:

$query = 
GLOBALS['TYPO3_DB']->SELECTquery('*','tx_boligtilbud_acceptet_offers','caseid='.$this->piVars['sagsnummer'].' 
AND user_id='.$this->piVars['userid'].'');
$res = $GLOBALS['TYPO3_DB']->sql(TYPO3_db, $query);

if(!mysql_num_rows($res)==0) {
               Do something...
}

I suddenly get this error:

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result 
resource in 
D:\Domains\initaaq.gl\wwwroot\typo3\typo3conf\ext\boligtilbud\pi1\class.tx_boligtilbud_pi1.php 
on line 56

Another thing. I have showphperrors set to 0 in the install tool. They 
shouldnt be displayed should they?

Im using typo3 3.8.1

/Brian Bendtsen