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

Question

I am getting this error when I pass an invalid SQL string... I spent the last hour trying to find the problem assuming - It\'s not my SQL it must be the db handle... ANyway, I\'

Answer 1

mysql_query will return false if there is an error

$result = mysql_query('select * from');
if ($result === false) {
    // caused by my invalid input above
} else {
    // process as usual
}

In fact, you're getting the error you describe because you're literally calling mysql_num_rows(false)