How to loop a MYSQL query / maybe in a function? - mysql

Question

What I've got so far is a code which updates one row as based on the IF conditions - but it
It is important that it is reliable and atomic (so with transaction).
It should loop/repeat itself based on #q which is quantity - however it can be in a MYSQL function rather than one fixed variable. How can I do that? I've added how the table should look like in the end
SET #q=1000;
SET #p=5.00;
SET #email='test#test.com';
update 1detail
SET quantity =
if((#q := quantity - #q) >= 0, #q, 0)
WHERE price>=#p ORDER BY datetime DESC LIMIT 1;
SET #q = if(#q <0,#q-#q-#q, #q);
UPDATE 1detail
SET quantity =
if(#q > 0, #q,quantity),
email=
if(#q > 0, #email, email)
WHERE price>=#p ORDER BY datetime DESC LIMIT 1;
The table at the beginning
quantity price email datetime
---------------------------------------------------
800 5.00 test1#test.com oldest
50 5.00 test2#test.com 2nd oldest
100 10.00 test3#test.com 3rd oldest (ignore in processing because #p < price)
How it should looks like after looping
quantity price email datetime
-----------------------------------------------------------------
0 5.00 test1#test.com oldest
150* 5.00 test#test.com (changed to #email) 2nd oldest (now newest)
100 10.00 test3#test.com 3rd oldest (ignored)
*this has changed as the oldest only had 800 and the 2nd oldest just had 50
So #q= 1000 (#q) - 800 (oldest) = 200
then #q = 200 (#q) - 50 (2nd oldest)
--> #q = 150
this updates the 2nd oldest row

Answer 1

A small loop can be achieved like this :
declare #counter int
set #counter=0
gohere:
set #counter=#counter+1
if #counter<10
BEGIN
select #counter
GOTO gohere;
END