Which is more ideal for updating each row at a time in a MySQL database?

Hi, can anyone recommend which of these is better for loading and updating one row at a time in a MySQL database? for() foreach() while() if...then() other...? What I am trying to do is make a PHP code open a table in a MySQL database, then it loads the information needed like Column 1 and Column 2 for example. Such as: Column 1 has 20 in one row and 15 in the next, Column 2 has 0 in both rows. What I got it to do is to subtract one value from Column 1 and add a value to Column 2. So after running this script once, it will end up as Column 1 having 19 for the first row and 14 for the row below it. And both rows in Column 2 having 1 in each. The problem starts when I try updating the database, rather than saving one at a time in each database it will replace all other rows with the first one loaded. So instead of row 2 having 14 it will have the same as the first row, which is 19. Thanks to Ross and hubo for the cookie advice, I have managed to get it working fine. If you can recommend anything that can get my one step closer to getting this script to parse successfully then it will be a great help, Many thanks again, Dan