计算工资

CREATE TABLE emp_bonus (empno INT , received DATE , TYPE INT);
INSERT  INTO emp_bonus VALUES( 7934, DATE '2005-5-17', 1 );
INSERT  INTO emp_bonus VALUES( 7934, DATE '2005-2-15', 2 );
INSERT  INTO emp_bonus VALUES( 7839, DATE '2005-2-15', 3 );
INSERT  INTO emp_bonus VALUES( 7782, DATE '2005-2-15', 1 );

员工的奖金的根据TYPE计算，TYPE1的奖金为员工工资的10%，TYPE2的奖金为员工工资的20%，TYPE3的奖金为员工工资的30%。
现要求返回上述员工也就是部门10的所有员工的工资及奖金。

SQL> SELECT e.deptno,
  2         e.empno,
  3         e.ename,
  4         e.sal,
  5         (e.sal * CASE
  6           WHEN eb.type = 1 THEN
  7            0.1
  8           WHEN eb.type = 2 THEN
  9            0.2
 10           WHEN eb.type = 3 THEN
 11            0.3
 12         END) AS bonus
 13    FROM emp e
 14   INNER JOIN emp_bonus eb ON (e.empno = eb.empno)
 15   WHERE e.deptno = 10
 16   ORDER BY 1, 2;

    DEPTNO      EMPNO ENAME             SAL      BONUS
---------- ---------- ---------- ---------- ----------
        10       7782 CLARK            2450        245
        10       7839 KING             5000       1500
        10       7934 MILLER           1300        130
        10       7934 MILLER           1300        260

SQL> SELECT eb.empno,
  2         (CASE
  3           WHEN eb.type = 1 THEN
  4            0.1
  5           WHEN eb.type = 2 THEN
  6            0.2
  7           WHEN eb.type = 3 THEN
  8            0.3
  9         END) AS rate
 10    FROM emp_bonus eb
 11   ORDER BY 1, 2;

     EMPNO       RATE
---------- ----------
      7782         .1
      7839         .3
      7934         .1
      7934         .2



SQL>  SELECT e.deptno,
  2         SUM(e.sal) AS total_sal,
  3         SUM(e.sal * CASE
  4               WHEN eb.type = 1 THEN
  5                0.1
  6               WHEN eb.type = 2 THEN
  7                0.2
  8               WHEN eb.type = 3 THEN
  9                0.3
 10             END) AS total_bonus
 11    FROM emp e
 12   INNER JOIN emp_bonus eb ON (e.empno = eb.empno)
 13   WHERE e.deptno = 10
 14   GROUP BY e.deptno;

    DEPTNO  TOTAL_SAL TOTAL_BONUS
---------- ---------- -----------
        10      10050        2135

此时MILLER 工资被计算了2次

正确写法:
SQL> SELECT e.deptno,
  2         SUM(e.sal) AS total_sal,
  3         SUM(e.sal * eb2.rate) AS total_bonus
  4    FROM emp e
  5   INNER JOIN (SELECT eb.empno,
  6                      SUM(CASE
  7                            WHEN eb.type = 1 THEN
  8                             0.1
  9                            WHEN eb.type = 2 THEN
 10                             0.2
 11                            WHEN eb.type = 3 THEN
 12                             0.3
 13                          END) AS rate
 14                 FROM emp_bonus eb
 15                GROUP BY eb.empno) eb2 ON eb2.empno = e.empno
 16   WHERE e.deptno = 10
 17   GROUP BY e.deptno;

    DEPTNO  TOTAL_SAL TOTAL_BONUS
---------- ---------- -----------
        10       8750        2135