Is there a way to reuse a calculated field within a mysql statement. I get the error "unknown column total_sale" for:
SELECT
s.f1 + s.f2 as total_sale,
s.f1 / total_sale as f1_percent
FROM sales s
or do I have to repeat the calculation, which would make for a very long SQL statement if I added all the calculations I need.
SELECT
s.f1 + s.f2 as total_sale,
s.f1 / (s.f1 + s.f2) as f1_percent
FROM sales s
of course I can do all the calculations in my php program.
Yes, you can reuse variables. This is how you do it:
SELECT
@total_sale := s.f1 + s.f2 as total_sale,
s.f1 / @total_sale as f1_percent
FROM sales s
Read more about it here: http://dev.mysql.com/doc/refman/5.0/en/user-variables.html
[Note: This behavior is undefined. According to the MySQL docs:]
As a general rule, you should never assign a value to a user variable and read the value within the same statement. You might get the results you expect, but this is not guaranteed.