Question

我要做的是添加另一列计算（cr - dr）

看到你无法在SELECT子句中重复使用别名，你将如何进行计算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，没有使用user variable更快？

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

Answer 3

您可以在＆＃34; total＆＃34;中重复计算。列。

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 ....

在SELECT中重用别名

3 个答案: