AVG（） 求平均数函数：

//求emp表中的sal属性的平均值mysql> select avg(sal) as salAverage from emp;+-------------+| salAverage |+-------------+| 2073.214286 |+-------------+1 row in set (0.11 sec)//emp表数据mysql> select * from emp;+-------+--------+-----------+------+------------+---------+---------+--------+| empno | ename | job | mgr | hiredate | sal | comm | deptno |+-------+--------+-----------+------+------------+---------+---------+--------+| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 || 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 || 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 || 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 || 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 || 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 || 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 || 7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 || 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 || 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 || 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 || 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 || 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 || 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 |+-------+--------+-----------+------+------------+---------+---------+--------+

SUM（）求和函数：

mysql> select sum(sal) as salSum from emp;+----------+| salSum |+----------+| 29025.00 |+----------+1 row in set (0.11 sec)

count（）计数函数：

//查看student表中的男女生人数mysql> select ssex,count(sage) from student group by ssex;+------+-------------+| ssex | count(sage) |+------+-------------+| M | 1 || 女 | 3 || 男 | 6 |+------+-------------+