sql - Is it possible to automaticly have in a row a substraction between two MYSQL variables -

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i have :

+----------+------+-----+--------+ | image_id | | bad | result | +----------+------+-----+--------+ |        1 |   10 |   2 |      x | +----------+------+-----+--------+ |        2 |    4 |   1 |      y | +----------+------+-----+--------+

where x , y calculated automaticaly respectively 10 - 2 , 4 - 1. (good - bad) -avoid negative number if possible-

i value change if values (good or bad) changes well.

+----------+------+-----+--------+ | image_id | | bad | result | +----------+------+-----+--------+ |        1 |   10 |   2 |      x | +----------+------+-----+--------+ |        2 |    4 |   1 |      y | +----------+------+-----+--------+

i can in php there way directly mysql ?

calculate result , return no less zero, avoiding negative numbers:

select image_id, good, bad, greatest(good-bad, 0) result `table`;

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