What I am trying to do is add another column that calculates (cr - dr)
Seeing as you cannot re-use an alias inside a SELECT clause, how would you go about calculatin
In SQL Server or Oracle, I'd use a CTE, but since you're using MySQL, you'd use a subquery:
SELECT dr, cr, cr + dr as total
FROM (
SELECT
SUM(b.bet_win * cy.fx_rate ) as dr,
SUM(b.bet_loss * cy.fx_rate ) as cr
FROM ....
WHERE ....) t;
EDIT: DOES NOT WORK. See comments. Isn't using a user variable faster in this case?
SELECT
@dr:=SUM(b.bet_win * cy.fx_rate ),
@cr:=SUM(b.bet_loss * cy.fx_rate ),
@cr+@dr as total
You can repeat the calculations in the "total" column.
SELECT
SUM(b.bet_win * cy.fx_rate) as dr,
SUM(b.bet_loss * cy.fx_rate) as cr,
SUM(b.bet_win * cy.fx_rate) + SUM(b.bet_loss * cy.fx_rate) as total
FROM ....
WHERE ....