mysql_num_rows无法正常工作

Question

I'm trying to check if the value of a mysql query returns false or actually contains a value. My first solution which worked properly looked like this:

    $gotTrailer = mysql_query("SELECT trailer FROM film_backup WHERE id='".key($countValues)."'");
    $iHasTrailer = mysql_fetch_array($gotTrailer);
    while(mysql_num_rows($gotTrailer)==''){
        next($countValues);
        $gotTrailer = mysql_query("SELECT trailer FROM film_backup WHERE id='".key($countValues)."'");
        $iHasTrailer = mysql_fetch_array($gotTrailer);
    }

This is a truly ugly solution, so I tried using mysql_num_rows() instead:

$gotTrailer = mysql_query("SELECT trailer FROM film_backup WHERE id='".key($countValues)."'");
    while(mysql_num_rows($gotTrailer)==0){
        next($countValues);
        $gotTrailer = mysql_query("SELECT trailer FROM film_backup WHERE id='".key($countValues)."'");
    }

But for whatever reason, this simply won't work. I tried using === false as well, but I geniunely don't know what's wrong. Hope you can help.

Answer 1

mysql_query() will return false only when it errors out. If the query returns an empty result, it still returns a resource (not false, empty, or 0).

mysql_fetch_array() will return false if there are no more rows, otherwise you are returned an array.

On a sidenote, these methods have been deprecated.

Resources: http://php.net/manual/en/function.mysql-query.php

http://www.php.net/manual/en/function.mysql-fetch-array.php

Answer 2

mysql_query returns false on error. If you want to check if there is an error on the query or not, you should check the return value of that function.

Now, if you want to check if there IS a result or not, mysql_num_rows will return >= 0 or false on error. So, your while should be

 while( (mysql_num_rows($gotTrailer) !== false) ){

Besides all this, the code has other flaws, next() could return false and the mysql_query will fail, also, remember to escape the queries to avoid SQL injection.

Answer 3

You can try with a For Loop as well

    $gotTrailer = mysql_query("SELECT trailer FROM film_backup WHERE id='".key($countValues)."'");

    for($i=0; $i<mysql_num_rows($gotTrailer); $i++)
    {
       next($countValues);
       $gotTrailer = mysql_query("SELECT trailer FROM film_backup WHERE id='".key($countValues)."'");
    }