标签：类型 count 1.3 3.3 _id mis bsp where res
1.可以对数值类型使用min，max，avg，sum：
SQL> select avg(salary),max(salary),min(salary),sum(salary)
2 from employees
3 where job_id like ‘%REP%‘;
AVG(SALARY) MAX(SALARY) MIN(SALARY) SUM(SALARY)
----------- ----------- ----------- -----------
8272.72727 11500 6000 273000
2.可以对数值型，日期型，字符型使用min，max函数：
SQL> select min(hire_date),max(hire_date)
2 from employees;
MIN(HIRE_ MAX(HIRE_
--------- ---------
13-JAN-01 21-APR-08
3.使用count函数
（1）count（*）返回表中行数：
SQL> select count(*)
2 from employees
3 where department_id=50;
COUNT(*)
----------
45
（2）COUNT(expr) 返回非空值的 expr 的行数：
SQL> select count(commission_pct)
2 from employees
3 where department_id=80;
COUNT(COMMISSION_PCT)
---------------------
34
（3）COUNT(DISTINCT expr) 返回 expr 非空且不重复的记录数。
SQL> select count(distinct department_id)
2 from employees;
COUNT(DISTINCTDEPARTMENT_ID)
----------------------------
11
（4）组函数忽略空值，NVL函数使分组函数无法忽略空值：
SQL> select avg(commission_pct)
2 from employees;
AVG(COMMISSION_PCT)
-------------------
.222857143
SQL> select avg(nvl(commission_pct,0))
2 from employees;
AVG(NVL(COMMISSION_PCT,0))
--------------------------
.072897196
（5）group by 字句：在SELECT 列表中所有未包含在组函数中的列都应该包含在GROUP BY 子句中。
SQL> select department_id,avg(salary)
2 from employees
3 group by department_id;
DEPARTMENT_ID AVG(SALARY)
------------- -----------
100 8601.33333
30 4150
7000
20 9500
70 10000
90 19333.3333
110 10154
50 3475.55556
40 6500
80 8955.88235
10 4400
DEPARTMENT_ID AVG(SALARY)
------------- -----------
60 5760
12 rows selected.
包含在 GROUP BY 子句中的列不必包含在SELECT 列表中：
SQL> select avg(salary)
2 from employees
3 group by department_id;
AVG(SALARY)
-----------
8601.33333
4150
7000
9500
10000
19333.3333
10154
3475.55556
6500
8955.88235
4400
AVG(SALARY)
-----------
5760
12 rows selected.
在 GROUP BY 子句中包含多个列：
SQL> select department_id dept_id,job_id,sum(salary)
2 from employees
3 group by department_id,job_id
4 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
DEPT_ID JOB_ID SUM(SALARY)
---------- ---------- -----------
80 SA_MAN 61000
80 SA_REP 243500
90 AD_PRES 24000
90 AD_VP 34000
100 FI_ACCOUNT 39600
100 FI_MGR 12008
110 AC_ACCOUNT 8300
110 AC_MGR 12008
SA_REP 7000
20 rows selected.
SQL>
标签：类型 count 1.3 3.3 _id mis bsp where res
原文地址：http://www.cnblogs.com/tomatoes-/p/6067512.html
