The problem of cookie

Hi all, I set the cookie and retrieve it at the same page but when I click botton twice, it only appear once. No matter how many times I click, it is always one time short. How can I solve this problem? When I click the botton, it will get the variable from cookie then connect to the database to retrive the data. But the value of the variable is always empty at the last time. When I checked the cookie, the variable got the value already. I don't know if I can set and retrieve cookie at the same page. Thanks a lot Dper