i agree with Karl, i cant be doing with sacrificing maintainable flexable code for the extra 0.0000000000000000000001 of performance, obviously you do need to think about performance issues but alot of it comes down to common sense i.e. calling count inside the for loop:
its just plain common sense, if you dont realise whats going on there and why it can potentially cause problems, just think about it either that rethink your life as a PHP programmer.

People do get carried away with themselves and come up with some retarded things that are barely readable but it saves that all important ms, winds me up, these are the same people who seem to be allergic to OOP, just because it can use more resources, done properly its not that much of a difference and its also maintainable and extend able so that you don't need to re produce code all the time, these days time of development is more costly than the hardware, but anyway ill stop myself there its another issue i have a bee in my bonnet about.

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mysql> SELECT * FROM `users` WHERE `users`.`clue` > 0;
Empty set (0.00 sec)