Oracle 分組函數用法示例詳解

聚合函數、多行函數、分組函數都是一類函數

GROUP BY 和 HAVING

group 函數：AVG\SUM\MIN\MAX\COUNT\STDDEV\VARIANCE

DISTINCT 與 group 函數結合使用

NULL 值在 group函數當中的處理

嵌套 group 函數

group 函數的文法：

SELECT GROUP_FUNCTION(COLUMN),...

FROM TABLE

[WHERE CONDITION]

[ORDER BY COLUMN];

---示例1：AVG\MAX\MIN\SUM針對NUMBER類型資料

SELECT AVG(SALARY), MAX(SALARY), MIN(SALARY), SUM(SALARY)

FROM EMPLOYEES

WHERE JOB_ID LIKE '%REP%';

AVG(SALARY) MAX(SALARY) MIN(SALARY) SUM(SALARY)

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

8272.72727 11500 6000 273000

---示例2：MIN和MAX可以針對number外還可以針對date類型資料

[email protected]> 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

[email protected]> SELECT COUNT(*) FROM EMPLOYEES;

COUNT(*)

----------

107

-----COUNT(*)傳回某個表中的行數

[email protected]> SELECT COUNT(1) FROM EMPLOYEES;

COUNT(1)

----------

107

---COUNT(EXPR)符合expr 的所有非空值行的行數，請看下例:

[email protected]> SELECT COUNT(COMMISSION_PCT) FROM EMPLOYEES;

COUNT(COMMISSION_PCT)

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

35

[email protected]> SELECT COUNT(DEPARTMENT_ID) FROM EMPLOYEES;

COUNT(DEPARTMENT_ID)

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

106

[email protected]> SELECT COUNT(EMPLOYEE_ID) FROM EMPLOYEES;

COUNT(EMPLOYEE_ID)

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

107

------------DISTINCT 和 group 函數的配合使用

示例：

[email protected]> SELECT COUNT(DISTINCT DEPARTMENT_ID) FROM EMPLOYEES;

COUNT(DISTINCTDEPARTMENT_ID)

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

11

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

-----------group 函數對 Null 值的處理

----group 函數忽略列中的 null 值

[email protected]> SELECT COUNT(COMMISSION_PCT) FROM EMPLOYEES;

COUNT(COMMISSION_PCT)

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

35

[email protected]> SELECT COUNT(NVL(COMMISSION_PCT,0)) FROM EMPLOYEES;

COUNT(NVL(COMMISSION_PCT,0))

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

107

-----35 人參與計算

[email protected]> SELECT AVG(COMMISSION_PCT) FROM EMPLOYEES;

AVG(COMMISSION_PCT)

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

.222857143

------107 人參與計算

[email protected]> SELECT AVG(NVL(COMMISSION_PCT,0)) FROM EMPLOYEES;

AVG(NVL(COMMISSION_PCT,0))

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

.072897196

-------建立分組資料----

GROUP BY 子句

計算每個部門中的平均薪水

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 必須包含在 GROUP BY 子句中

列出的單行必須包含在 group by 子句中

執行順序，先計算 WHERE,後計算group by，再查詢結果，最後執行 order by

order by 中可以使用别名，where 和 group by 中不允許使用别名

在 SELECT 清單中出現的所有列，隻要不在 group 函數中，都必須包含在

group by 子句中。

示例：按照部門分組，把每個部門的平均工資統計出來

SELECT DEPARTMENT_ID,AVG(SALARY)

FROM EMPLOYEES

GROUP BY DEPARTMENT_ID

ORDER BY DEPARTMENT_ID;

DEPARTMENT_ID AVG(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.

-------------重點：進階用法

使用 group by 對多列進行分組

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 函數的非法使用示例：

示例1：

[email protected]> 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

------必須加一個 group by 子句，包含 DEPARTMENT_ID

示例2：

[email protected]> 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

-------必須在 GROUP BY 子句中加上 JOB_ID

-------不得在 WHERE 子句中限制 groups

可以考慮使用 HAVING 子句來限制 groups

SELECT DEPARTMENT_ID, AVG(SALARY)

FROM EMPLOYEES

WHERE AVG(SALARY) > 8000

GROUP BY DEPARTMENT_ID;

WHERE AVG(SALARY) > 8000

*

ERROR at line 3:

ORA-00934: group function is not allowed here

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

---------HAVING 子句

文法：先 group by，然後 group function，然後 Having

SELECT COLUMN,GROUP_FUNCTION

FROM TABLE

[WHERE CONDITION]

[GROUP BY GROUP_BY_EXPRESSION]

[HAVING GROUP_CONDITION]

[ORDER BY COLUMN];

示例：HAVING 子句

SELECT DEPARTMENT_ID, MAX(SALARY)

FROM EMPLOYEES

GROUP BY DEPARTMENT_ID

HAVING MAX(SALARY) > 10000;

DEPARTMENT_ID MAX(SALARY)

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

100 12000

30 11000

90 24000

20 13000

110 12000

80 14000

-------執行順序：SELECT\FROM \ WHERE \GROUP BY \HAVING \ORDER BY

SELECT JOB_ID, SUM(SALARY) PAYROLL

FROM EMPLOYEES

WHERE JOB_ID NOT LIKE '%REP%'

GROUP BY JOB_ID

HAVING 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 函數的嵌套

最後一個示例：

SELECT MAX(AVG(SALARY))

FROM EMPLOYEES

GROUP BY DEPARTMENT_ID;

SELECT MAX(AVG(SALARY))

FROM EMPLOYEES

GROUP BY DEPARTMENT_ID;

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本文來源：http://blog.csdn.net/xiangsir/article/details/8604794