在SELECT中重用别名

Question

我想要做的是添加另一个计算的列(cr - dr)

看到你不能在SELECT子句中重用别名,你会怎么做计算 total

    SELECT SUM(b.bet_win * cy.fx_rate )as dr, SUM(b.bet_loss * cy.fx_rate ) as cr, cr+dr as total
    FROM ....
    WHERE ....

Answer 1

在SQL Server或Oracle中,我使用CTE,但由于您使用的是MySQL,因此您将使用子查询:

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;

Answer 2

编辑:不工作.看评论.在这种情况下,是不是更快地使用用户变量？

SELECT
  @dr:=SUM(b.bet_win * cy.fx_rate ),
  @cr:=SUM(b.bet_loss * cy.fx_rate ), 
  @cr+@dr as total