SQL基本操作（3）--聚合函数查询

1、COUNT()函数

SELECT COUNT(*) FROM t_grade;

SELECT COUNT(*) AS total FROM t_grade;

SELECT stuName,COUNT(*) FROM t_grade GROUP BY stuName;

2、SUM()函数

3、AVG()函数

SELECT stuName,AVG(score) FROM t_grade WHERE stuName="张三";

SELECT stuName,AVG(score) FROM t_grade GROUP BY stuName;

4、MAX()函数

SELECT stuName,course,MAX(score) FROM t_grade WHERE stuName="张三";

SELECT stuName,MAX(score) FROM t_grade GROUP BY stuName;

5、MIN()函数

SELECT stuName,course,MIN(score) FROM t_grade WHERE stuName="张三";

SELECT stuName,MIN(score) FROM t_grade GROUP BY stuName;