ช่วยดูหน่อยคะ error: Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in C แต่พอขึ้น serv มันได้ซะงั้น ทำใน localhost มันขึ้น error

$strSQL ="SELECT s_class.scode, student.sid,student.stname,student.sname, student.ssname, student.sex, s_class.ccode, s_class.RCODE, room.rname'
        . ' FROM ( s_class INNER JOIN student ON s_class.scode = student.scode )  INNER JOIN room ON s_class.rcode = room.rcode  WHERE  s_class.year =CONVERT( _utf8 '$ed_year' USING tis620 ) AND room.rname=CONVERT( _utf8 '$ed_class' USING tis620 )  AND s_class.turm=CONVERT( _utf8 '$ed_termChang' USING tis620 ) order by s_class.scode ";		
//echo $strSQL;
$objQuery = mysql_query($strSQL);
$resultData = array();
for ($i=0;$i<mysql_num_rows($objQuery);$i++) {
    $result = mysql_fetch_array($objQuery);
    array_push($resultData,$result);
}