不同粒度的计算SQL--以计算员工的工资为例

创建 emp_bonus-奖金表 并插入数据

CREATE TABLE emp_bonus
(
empno VARCHAR(10),
received DATE,
TYPE CHAR(5)
)

INSERT INTO emp_bonus(empno,received,TYPE) VALUES
 ('7934', '2017-05-17','1'),
 ('7934', '2017-02-15','2'),
 ('7839', '2017-02-15','3'),
 ('7782', '2017-02-15','1')

创建 emp-员工表 并插入数据

CREATE TABLE emp
(
empno VARCHAR(10),
ename VARCHAR(10),
deptno CHAR(5),
sal CHAR(8)
)

INSERT INTO emp(empno,ename,deptno,sal) VALUES
 ('7934', 'miller','10','1300'),
 ('7839', 'king','10','5000'),
 ('7782', 'clark','10','2450')

根据用户的类型来发奖金，1 * 0.1; 2 * 0.2 ,3 * 0.3
 SELECT a.empno,a.ename,a.deptno,a.sal,(CASE WHEN b.type= 1 THEN a.sal*0.1
                                             WHEN b.type= 2 THEN a.sal*0.2
                                             WHEN b.type= 3 THEN a.sal*0.3 END) bonus
   FROM emp a 
   JOIN emp_bonus b
     ON a.empno=b.empno

要求计算:共发了多少工资和奖金
PS : 难点在于不同粒度的sum
方法一：

SELECT SUM(c.sal) ,SUM(c.bonus)
FROM (  SELECT z.empno,MAX(z.sal) sal,SUM(z.bonus) bonus
          FROM ( SELECT a.empno,a.ename,a.deptno,a.sal
                       ,(CASE WHEN b.type= 1 THEN a.sal*0.1
                              WHEN b.type= 2 THEN a.sal*0.2
                              WHEN b.type= 3 THEN a.sal*0.3 END) bonus
           FROM emp a 
           JOIN emp_bonus b
             ON a.empno=b.empno) z
     GROUP BY z.empno
      )c

方法二：

SELECT SUM(a.sal),SUM(a.sal*b.rate)
  FROM emp a
  JOIN ( SELECT empno,SUM(CASE WHEN TYPE= 1 THEN 0.1
                               WHEN TYPE= 2 THEN 0.2
                               WHEN TYPE= 3 THEN 0.3 END) AS rate
          FROM emp_bonus
         GROUP BY empno)b
    ON a.empno=b.empno
 GROUP BY a.deptno