mysql_num_rows() expects parameter 1 to be resource

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PHP

Hello Guys,

Can you help me on how to solve this error? I've search on Google for a day but still no luck, so far this is my code.

function updatePackages(){
    if(isset($_GET["id"])) {
        $rowId = mysql_real_escape_string(htmlentities($_GET["id"]));
        $sql = mysql_query("SELECT * FROM packages WHERE id='$rowId' LIMIT 1");
        $countRow = mysql_num_rows($sql);
        if($countRow > 0){
            echo "SOMETHING";
        } 
    }
}

Thanks,
Athan