Question

I encountered a situation in which I have to call a function several times inside a view. something like:

select a,b,c, GetRefund(a) AS REFUND, d-GetRefund(a) AS Payment_left FROM bla bla bla.

Obviously I can’t join the refunds table to this view (or else I’d do it).
It seems the explain plan doesn’t consider the function’s cause no matter how many times I use them, explain looks the same.

What I’m asking is – does MYSQL optimize this and actually call the function a single time?
is there a better solution for doing this?
Thank you very much!

Answer 1

No. MySQL calls this function twice for each selected row

Is there a better solution? We’d need to know a bit more about your database structure, but something like this should reduce it to one function call per row:

SELECT 
  a,b,c, REFUND, d-REFUND AS PaymentLeft 
FROM (
  select a,b,c,d, GetRefund(a) AS REFUND FROM bla bla bla
) AS sq