Array How To ???

Hello Everyone, I would like to sort a list of array indices. The array is multi- dimensional N x 3 for example, if (note the actual data is not important to my question): $a[0]['a'] = 1, $a[0]['b'] = 2, $a[0]['c'] = 3 $a[1]['a'] = 1, $a[1]['b'] = 2, $a[1]['c'] = 3 $a[2]['a'] = 1, $a[2]['b'] = 2, $a[2]['c'] = 3 Q1) I will use the "usort" user sort function. I see the example for multi-dimensional arrays in the manual (they use fruits, not a b c). Does usort work in Windows (NT4 machine, PHP 4.04, running as cgi) ? Q2) The array $a will be stored in a session. I will want to clear $a and then recreate and resort $a. How do I clear a variable or array ? For example, if the first time I create $a it gets up to $a[30] (remember $a is saved in a session), but if I recreate $a and the indices only go to $a[20], I need to be sure $a[21] to $a[30] no longer exist. Easiest way: clear $a before recreating it. Q3) The $a array will be generated from the results of a mysql database query. Is it realistic to save the results set ($res) of a query ($res = mysql_query($sql)) in a session? I think the size of $res won't exceed 32KB. Is there a session storage size limit for Windows? Thanks very much for your experience, Barry.