多行函数(sum,count,avg,having和where的区别)

SQL> host cls

SQL> –工资总额

SQL> select sum(sal) from emp;

SUM(SAL)

29025

SQL> –员工人数

SQL> select count(*) from emp;

COUNT(*)

14

SQL> –平均工资

SQL> select sum(sal)/count(*) 一, avg(sal) 二 from emp;

一         二

2073.21429 2073.21429

SQL> –平均奖金

SQL> select sum(comm)/count(*) 一, sum(comm)/count(comm) 二, avg(comm) 三 from emp;

一         二         三

157.142857 550 550

SQL> –空值 4. 组函数会自动滤空

SQL> select count(*),count(comm) from emp;

COUNT(*) COUNT(COMM)

14           4

SQL> select count(*),count(nvl(comm,0)) from emp;

COUNT(*) COUNT(NVL(COMM,0))

    14             14

SQL> –可以在组函数中嵌套滤空函数，来屏蔽组函数的滤空功能

SQL> host cls

SQL> –求各个部门的平均工资

SQL> set linesize 150

SQL> col sal for 9999

SQL> select * from emp;

EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO

7369 SMITH      CLERK           7902 17-12月-80       800                    20
7499 ALLEN      SALESMAN        7698 20-2月 -81      1600        300         30
7521 WARD       SALESMAN        7698 22-2月 -81      1250        500         30
7566 JONES      MANAGER         7839 02-4月 -81      2975                    20
7654 MARTIN     SALESMAN        7698 28-9月 -81      1250       1400         30
7698 BLAKE      MANAGER         7839 01-5月 -81      2850                    30
7782 CLARK      MANAGER         7839 09-6月 -81      2450                    10
7788 SCOTT      ANALYST         7566 13-7月 -87      3000                    20
7839 KING       PRESIDENT            17-11月-81      5000                    10
7844 TURNER     SALESMAN        7698 08-9月 -81      1500          0         30
7876 ADAMS      CLERK           7788 13-7月 -87      1100                    20

EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO

7900 JAMES      CLERK           7698 03-12月-81       950                    30
7902 FORD       ANALYST         7566 03-12月-81      3000                    20
7934 MILLER     CLERK           7782 23-1月 -82      1300                    10

已选择14行。

SQL> select deptno,avg(sal)

2 from emp

3 group by depnto;

group by depnto

*

第 3 行出现错误:

ORA-00904: “DEPNTO”: 标识符无效

SQL> ed

已写入 file afiedt.buf

1 select deptno,avg(sal)

2 from emp

3* group by deptno

SQL> /

DEPTNO   AVG(SAL)

30 1566.66667
20       2175
10 2916.66667

SQL> –语法

SQL> select deptno,job,avg(sal)

2 from emp

3 group by depnto;

group by depnto

*

第 3 行出现错误:

ORA-00904: “DEPNTO”: 标识符无效

SQL> ed

已写入 file afiedt.buf

1 select deptno,job,avg(sal)

2 from emp

3* group by deptno

SQL> /

select deptno,job,avg(sal)

*

第 1 行出现错误:

ORA-00979: 不是 GROUP BY 表达式

SQL> ed

已写入 file afiedt.buf

1 select deptno,job,avg(sal)

2 from emp

3* group by deptno,job

SQL> –group by多列：先按照第一列分；如果第一列相同，再按照第二列分

SQL> ed

已写入 file afiedt.buf

1 select deptno,job,avg(sal)

2 from emp

3 group by deptno,job

4* order by 1

SQL> /

DEPTNO JOB         AVG(SAL)

10 CLERK           1300
10 MANAGER         2450
10 PRESIDENT       5000
20 ANALYST         3000
20 CLERK            950
20 MANAGER         2975
30 CLERK            950
30 MANAGER         2850
30 SALESMAN        1400

已选择9行。

SQL> –按部门，不同的职位统计平均工资

SQL> host cls

SQL> –having

SQL> select deptno,avg(sal)

2 from emp

3 group by depnto;

group by depnto

*

第 3 行出现错误:

ORA-00904: “DEPNTO”: 标识符无效

SQL> ed

已写入 file afiedt.buf

1 select deptno,avg(sal)

2 from emp

3* group by deptno

SQL> /

DEPTNO   AVG(SAL)

30 1566.66667
20       2175
10 2916.66667

SQL> –查询平均工资大于2000的部门

SQL> ed

已写入 file afiedt.buf

1 select deptno,avg(sal)

2 from emp

3 group by deptno

4* having avg(sal)>2000

SQL> /

DEPTNO   AVG(SAL)

20       2175
10 2916.66667

SQL> –having 过滤分组

SQL> host cls

SQL> –having和where的区别

SQL> –求10号部门的平均工资

SQL> select deptno,avg(sal)

2 from emp

3 group by deptno

4 having deptno=10;

DEPTNO   AVG(SAL)

10 2916.66667

SQL> select deptno,avg(sal)

2 from emp

3 where deptno=10

4 group by deptno;

DEPTNO   AVG(SAL)

10 2916.66667

SQL> --SQL优化 3. 尽量使用where

SQL> 例外：如果条件中含义组函数，只能使用having

SP2-0734: 未知的命令开头 “例外：如果…” - 忽略了剩余的行。

SQL> – 例外：如果条件中含义组函数，只能使用having

SQL> host cls

SQL> –group by的增强

SQL> /*

SQL> group by deptno,job

SQL> +

SQL> group by deptno

SQL> +

SQL> group by null

SQL>

SQL> =

SQL>

SQL> group by rollup(deptno,job)

SQL>

SQL> group by rollup(a,b)

SQL> =

SQL> group by a,b

SQL> +

SQL> group by a

SQL> +

SQL> group by null

SQL>

SQL> */

SQL> select deptno,job,sum(sal)

2 from emp

3 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> –SQLPLUS支持报表功能

SQL> break on deptno skip 2

SQL> select deptno,job,sum(sal)

2 from emp

3 group by rollup(deptno,job);

DEPTNO JOB         SUM(SAL)

    10 CLERK           1300
MANAGER         2450
PRESIDENT       5000
8750

20 CLERK           1900
ANALYST         6000
MANAGER         2975
10875

DEPTNO JOB         SUM(SAL)

30 CLERK            950
MANAGER         2850
SALESMAN        5600
9400

29025

已选择13行。

SQL> break on null

SQL> /

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> spool off