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adding / subtracting values, preventing the field to roll over?


Lashiec

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I've got a field (int) and I need to add/subtract numbers from it for a shopping cart quantity field. The thing is, I can update the column with add/subtracted values, but if the value is 4 and I subtract 5 from it, it rolls over to 16475715 (it's unsigned). Is there a way to produce an error so that if it goes below 0, or above the maximum number, it won't do the update and will send an error out?

 

Or... Should I just read the value out (4), do my math with PHP ($val = $val - 5), and then check if $val is within a reasonable range (0 to 16475715). I guess this way $val would become -1 and then error out since it's below 0 and all...

 

Any ideas?

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