Oracle 分组函数用法示例详解

聚合函数、多行函数、分组函数都是一类函数

GROUP BY 和 H***ING

group 函数：***G\SUM\MIN\MAX\COUNT\STDDEV\VARIANCE

DISTINCT 与 group 函数结合使用

NULL 值在 group函数当中的处理

嵌套 group 函数

group 函数的语法：

SELECT GROUP_FUNCTION(COLUMN),...

FROM TABLE

[WHERE CONDITION]

[ORDER BY COLUMN];

---示例1：***G\MAX\MIN\SUM针对NUMBER类型数据

SELECT ***G(SALARY), MAX(SALARY), MIN(SALARY), SUM(SALARY)

FROM EMPLOYEES

WHERE JOB_ID LIKE '%REP%';

***G(SALARY) MAX(SALARY) MIN(SALARY) SUM(SALARY)

----------- ----------- ----------- -----------

8272.72727 11500 6000 273000



---示例2：MIN和MAX可以针对number外还可以针对date类型数据

hr@PROD> SELECT MIN(HIRE_DATE), MAX(HIRE_DATE) FROM EMPLOYEES;

MIN(HIRE_ MAX(HIRE_

--------- ---------

17-JUN-87 21-APR-00

----示例3：COUNT(*) 和 COUNT(1),COUNT(1)的速度比COUNT(*)快

hr@PROD> SELECT COUNT(*) FROM EMPLOYEES;

COUNT(*)

----------

107

-----COUNT(*)返回某个表中的行数

hr@PROD> SELECT COUNT(1) FROM EMPLOYEES;

COUNT(1)

----------

107



---COUNT(EXPR)符合expr 的所有非空值行的行数，请看下例:

hr@PROD> SELECT COUNT(COMMISSION_PCT) FROM EMPLOYEES;

COUNT(COMMISSION_PCT)

---------------------

35

hr@PROD> SELECT COUNT(DEPARTMENT_ID) FROM EMPLOYEES;

COUNT(DEPARTMENT_ID)

--------------------

106

hr@PROD> SELECT COUNT(EMPLOYEE_ID) FROM EMPLOYEES;

COUNT(EMPLOYEE_ID)

------------------

107



------------DISTINCT 和 group 函数的配合使用

示例：

hr@PROD> SELECT COUNT(DISTINCT DEPARTMENT_ID) FROM EMPLOYEES;

COUNT(DISTINCTDEPARTMENT_ID)

----------------------------

11



--------------------------------

-----------group 函数对 Null 值的处理

----group 函数忽略列中的 null 值

hr@PROD> SELECT COUNT(COMMISSION_PCT) FROM EMPLOYEES;

COUNT(COMMISSION_PCT)

---------------------

35

hr@PROD> SELECT COUNT(NVL(COMMISSION_PCT,0)) FROM EMPLOYEES;

COUNT(NVL(COMMISSION_PCT,0))

----------------------------

107



-----35 人参与计算

hr@PROD> SELECT ***G(COMMISSION_PCT) FROM EMPLOYEES;

***G(COMMISSION_PCT)

-------------------

.222857143

------107 人参与计算

hr@PROD> SELECT ***G(NVL(COMMISSION_PCT,0)) FROM EMPLOYEES;

***G(NVL(COMMISSION_PCT,0))

--------------------------

.072897196

-------创建分组数据----

GROUP BY 子句

计算每个部门中的平均薪水

SELECT COLUMN ,GROUP_FUNCTION(COLUMN)

FROM TABLE

[WHERE CONDITION]

[GROUP BY GROUP_BY_EXPRESSION]

[ORDER BY COLUMN];

注意：SELECT 子句中的 COLUMN 必须包含在 GROUP BY 子句中

列出的单行必须包含在 group by 子句中

执行顺序，先计算 WHERE,后计算group by，再查询结果，最后执行 order by

order by 中可以使用别名，where 和 group by 中不允许使用别名

在 SELECT 列表中出现的所有列，只要不在 group 函数中，都必须包含在

group by 子句中。

示例：按照部门分组，把每个部门的平均工资统计出来

SELECT DEPARTMENT_ID,***G(SALARY)

FROM EMPLOYEES

GROUP BY DEPARTMENT_ID

ORDER BY DEPARTMENT_ID;

DEPARTMENT_ID ***G(SALARY)

------------- -----------

10 4400

20 9500

30 4150

40 6500

50 3475.55556

60 5760

70 10000

80 8955.88235

90 19333.3333

100 8600

110 10150

7000

12 rows selected.

-------------重点：高级用法

使用 group by 对多列进行分组

SELECT DEPARTMENT_ID DEPT_ID, JOB_ID,SUM(SALARY)

FROM EMPLOYEES

GROUP BY DEPARTMENT_ID, JOB_ID

ORDER BY DEPARTMENT_ID;

DEPT_ID JOB_ID SUM(SALARY)

---------- ---------- -----------

10 AD_ASST 4400

20 MK_MAN 13000

20 MK_REP 6000

30 PU_CLERK 13900

30 PU_MAN 11000

40 HR_REP 6500

50 SH_CLERK 64300

50 ST_CLERK 55700

50 ST_MAN 36400

60 IT_PROG 28800

70 PR_REP 10000

80 SA_MAN 61000

80 SA_REP 243500

90 AD_PRES 24000

90 AD_VP 34000

100 FI_ACCOUNT 39600

100 FI_MGR 12000

110 AC_ACCOUNT 8300

110 AC_MGR 12000

SA_REP 7000



-------GROUP 函数的非法使用示例：

示例1：

hr@PROD> SELECT DEPARTMENT_ID,COUNT(LAST_NAME)

2 FROM EMPLOYEES;

SELECT DEPARTMENT_ID,COUNT(LAST_NAME)

*

ERROR at line 1:

ORA-00937: not a single-group group function

------必须加一个 group by 子句，包含 DEPARTMENT_ID

示例2：

hr@PROD> SELECT DEPARTMENT_ID, JOB_ID,COUNT(LAST_NAME)

2 FROM EMPLOYEES

3 GROUP BY DEPARTMENT_ID;

SELECT DEPARTMENT_ID, JOB_ID,COUNT(LAST_NAME)

*

ERROR at line 1:

ORA-00979: not a GROUP BY expression

-------必须在 GROUP BY 子句中加上 JOB_ID

-------不得在 WHERE 子句中限制 groups

可以考虑使用 H***ING 子句来限制 groups

SELECT DEPARTMENT_ID, ***G(SALARY)

FROM EMPLOYEES

WHERE ***G(SALARY) > 8000

GROUP BY DEPARTMENT_ID;

WHERE ***G(SALARY) > 8000

*

ERROR at line 3:

ORA-00934: group function is not allowed here

------------------------------------

---------H***ING 子句

语法：先 group by，然后 group function，然后 Having

SELECT COLUMN,GROUP_FUNCTION

FROM TABLE

[WHERE CONDITION]

[GROUP BY GROUP_BY_EXPRESSION]

[H***ING GROUP_CONDITION]

[ORDER BY COLUMN];

示例：H***ING 子句

SELECT DEPARTMENT_ID, MAX(SALARY)

FROM EMPLOYEES

GROUP BY DEPARTMENT_ID

H***ING MAX(SALARY) > 10000;

DEPARTMENT_ID MAX(SALARY)

------------- -----------

100 12000

30 11000

90 24000

20 13000

110 12000

80 14000



-------执行顺序：SELECT\FROM \ WHERE \GROUP BY \H***ING \ORDER BY


SELECT JOB_ID, SUM(SALARY) PAYROLL

FROM EMPLOYEES

WHERE JOB_ID NOT LIKE '%REP%'

GROUP BY JOB_ID

H***ING SUM(SALARY) > 13000

ORDER BY SUM(SALARY);

JOB_ID PAYROLL

---------- ----------

PU_CLERK 13900

AD_PRES 24000

IT_PROG 28800

AD_VP 34000

ST_MAN 36400

FI_ACCOUNT 39600

ST_CLERK 55700

SA_MAN 61000

SH_CLERK 64300

-------------GROUP 函数的嵌套

最后一个示例：

SELECT MAX(***G(SALARY))

FROM EMPLOYEES

GROUP BY DEPARTMENT_ID;

SELECT MAX(***G(SALARY))

FROM EMPLOYEES

GROUP BY DEPARTMENT_ID;

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