Mysql 第六天 使用聚合函数查询

5.1     count()函数

SELECT COUNT(*) FROM t_grade;

SELECT COUNT(*) AS total FROM t_grade;

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

5.2     sum函数

SELECT stuName,SUM(score) FROM t_grade WHERE stuName = '张三'

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

5.3     avg函数

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

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

5.4     max函数

SELECT stuName,MAX(score) FROM t_grade WHERE stuName = '张三'

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

5.5     min函数

SELECT stuName,MIN(score) FROM t_grade WHERE stuName = '张三'

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