oracle_集合函数

 查询10和20号部门的员工
SQL> 1. select * from emp where deptno in (10,20);
SQL> 2. select * from emp where deptno=10 or deptno=20;
SQL> 3. 集合运算
SQL>    select * from emp where deptno=10
SQL>      加上
SQL>    select * from emp where deptno=20
SQL> */
SQL> select * from emp where deptno=10
  2  union
  3  select * from emp where deptno=20;

     EMPNO ENAME      JOB              MGR HIREDATE              SAL       COMM     DEPTNO
---------- ---------- --------- ---------- -------------- ---------- ---------- ----------
      7369 SMITH      CLERK           7902 17-12月-80            800                    20
      7566 JONES      MANAGER         7839 02-4月 -81           2975                    20
      7782 CLARK      MANAGER         7839 09-6月 -81           2450                    10
      7788 SCOTT      ANALYST         7566 19-4月 -87           3000                    20
      7839 KING       PRESIDENT            17-11月-81           5000                    10
      7876 ADAMS      CLERK           7788 23-5月 -87           1100                    20
      7902 FORD       ANALYST         7566 03-12月-81           3000                    20
      7934 MILLER     CLERK           7782 23-1月 -82           1300                    10                                                                                                              

已选择 8 行。

SQL> host cls

SQL> select deptno,job,sum(sal) from emp group by rollup(deptno,job);

    DEPTNO JOB         SUM(SAL)
---------- --------- ----------
        10 CLERK           1300
        10 MANAGER         2450
        10 PRESIDENT       5000
        10                 8750
        20 CLERK           1900
        20 ANALYST         6000
        20 MANAGER         2975
        20                10875
        30 CLERK            950
        30 MANAGER         2850
        30 SALESMAN        5600                                                                                                                                                                         

    DEPTNO JOB         SUM(SAL)
---------- --------- ----------
        30                 9400
                          29025                                                                                                                                                                         

已选择 13 行。

SQL>  select deptno,job,sum(sal) from emp group by deptno,job
  2   union
  3   select deptno,sum(sal) from emp group by deptno
  4   union
  5   select sum(sal) from emp;
 select deptno,sum(sal) from emp group by deptno
 *
第 3 行出现错误:
ORA-01789: 查询块具有不正确的结果列数 

SQL> /*
SQL> 注意的问题：
SQL> 1.参与运算的各个集合必须列数相同且类型一致
SQL> 2. 采用第一个集合作为最后的表头
SQL> 3. order by 永远在最后
SQL> 4. 括号
SQL> */
SQL>  select deptno,job,sum(sal) from emp group by deptno,job
  2   union
  3   select deptno,to_char(null),sum(sal) from emp group by deptno
  4   union
  5   select to_number(null),to_char(null),sum(sal) from emp;

    DEPTNO JOB         SUM(SAL)
---------- --------- ----------
        10 CLERK           1300
        10 MANAGER         2450
        10 PRESIDENT       5000
        10                 8750
        20 ANALYST         6000
        20 CLERK           1900
        20 MANAGER         2975
        20                10875
        30 CLERK            950
        30 MANAGER         2850
        30 SALESMAN        5600                                                                                                                                                                         

    DEPTNO JOB         SUM(SAL)
---------- --------- ----------
        30                 9400
                          29025                                                                                                                                                                         

已选择 13 行。

SQL> --break on deptno skip 2
SQL> host cls

SQL> --SQL执行时间
SQL> set timing on
SQL> select deptno,job,sum(sal) from emp group by rollup(deptno,job);

    DEPTNO JOB         SUM(SAL)
---------- --------- ----------
        10 CLERK           1300
        10 MANAGER         2450
        10 PRESIDENT       5000
        10                 8750
        20 CLERK           1900
        20 ANALYST         6000
        20 MANAGER         2975
        20                10875
        30 CLERK            950
        30 MANAGER         2850
        30 SALESMAN        5600                                                                                                                                                                         

    DEPTNO JOB         SUM(SAL)
---------- --------- ----------
        30                 9400
                          29025                                                                                                                                                                         

已选择 13 行。

已用时间:  00: 00: 00.02
SQL>  select deptno,job,sum(sal) from emp group by deptno,job
  2   union
  3   select deptno,to_char(null),sum(sal) from emp group by deptno
  4   union
  5   select to_number(null),to_char(null),sum(sal) from emp;

    DEPTNO JOB         SUM(SAL)
---------- --------- ----------
        10 CLERK           1300
        10 MANAGER         2450
        10 PRESIDENT       5000
        10                 8750
        20 ANALYST         6000
        20 CLERK           1900
        20 MANAGER         2975
        20                10875
        30 CLERK            950
        30 MANAGER         2850
        30 SALESMAN        5600                                                                                                                                                                         

    DEPTNO JOB         SUM(SAL)
---------- --------- ----------
        30                 9400
                          29025                                                                                                                                                                         

已选择 13 行。

已用时间:  00: 00: 00.04
SQL> --SQL 优化 5. 尽量不要使用集合运算
SQL> set timing off
SQL> spool off