MySQL & PHP Parameter 1 as Resource

Question

Alright, PHP is throwing this error at me (in the log) when I run the code mentioned below:

Error

mysql_num_rows() expects pa

Answer 1

As it been said, you're missing mysql_query function.
Though whole approach is wrong. You shouldn't select whole load of ata if you need only number of rows.
So, it must be

$sql = "SELECT count(*) FROM db";
$res = mysql_query($sql) or trigger_error(mysql_error().$sql);
$row = mysql_fetch_row($res);
$countFP = $row[0];
$aID = rand(1, $countFP);

And I hope you won't use $aID for any database related action