How do i use similiar to assign operator += in sql?

Question

i can only think one way, SELECT FROM WHERE and save it in variable (PHP), add it, and UPDATE, done.

the problem is, i need do it many times in one file, so, i scared it will not good to performance, can someone give me idea/your suggestion? anything is fine.

#what i know is, mysql only have := as assign operator

#may be it's just me, i try search at forum (like stackoverflow), but still not find it

Answer 1

i only test it at intepreter online, and it work,

#ex: id int
UPDATE test SET id=id+11 WHERE id=2

#never i think about it, i'm so stupid.
#i too focus at mysql that only have := as assign operator

Answer 2

$a=3;
$a+=4; //Solving it: $a=3+4
echo $a;

Output: 7. Now $a is 7.

+= obtains the new value for a variable