PHP transaction issue ( using 'for update')

[Mark Procter]

Hi I've got a bit of a problem trying to get the functionality I want working with my university project.

I've created a 'records update' page where the variables are selected within a transaction, like this:

mysql_query("begin");

$sql = "SELECT * FROM animal WHERE animal_id = '$thisAnimal_id' for update";

$result = MYSQL_QUERY($sql);
$numberOfRows = MYSQL_NUMROWS($result);
if ($numberOfRows==0) {
?>
...ect

(NB The 'commit' is not done on this page but on the post-to page of the form on this page.)

I want to create this scenario: when a user has selected this animal for update and is in the process of changing variables in the form, another user cannot select the same animal. I thought this was possible with the 'for update' clause of the select request but it seems that other users are still able to select the same animal and get all the variables from the db??

I know that its not logical to have the commit on the post page but seen as its all part of the same transaction i don't see why this isn't possible.

Please can someone shed some light on my error?

Thanks in advance.

PS. I'm using mysql5 and innodb tables btw! I know that transactions work where the begin and commit are on the same page but I can't see a way of doing that in this case.