根据条件在同一列和同一列上执行减法

Question

我有一个具有以下结构的表：

employeeid  SalaryType  Amount
------------------------------
100         w           200
100         s           100
210         w           300
210         s           50
300         w           90
300         s           30

根据这些条目，我想检索以下结果：

emloyeeid   Amount (difference between W and S)
-----------------------------------------------
100         100
210         250
300         60

我如何实现这一结果？

Answer 1

例如......

SELECT t1.employeeid, t1.amount - t2.amount FROM 
  (SELECT * FROM tablename WHERE salaryType = 'w') t1,
  (SELECT * FROM tablename WHERE salaryType = 's') t2
WHERE t1.employeeid = t2.employeeid  

Answer 2

您可以使用LEFT JOIN来解决问题

SELECT employeeid, t1.amount - t2.amount FROM
mytable AS t1 LEFT JOIN mytable AS t2 
ON t1.employeeid = t2.employeeid 
AND t1.SalaryType = 'w' AND t2.SalaryType = 's'