count 统计总数
select count(*) as 女性人数 from student where gender='女';//查询女性总人数max最大值
select max(age) as 年龄最大 from student; select max(height) from student where gender='女';//查询最高身高的女性sum 求和
select sum(age) from student;//所有人的年龄总和avg 平均值
select avg(age) from student;//所有人的年龄平均值round 四舍五入 round(123.23,2)小数点保留2位
select round(avg(height),2) from student where gender='男';//计算男性平均身高 保留2位小数分组一般与聚合函数一起使用 计算每种性别的人数
select gender,count(*) from student group by gender;计算男性人数
select gender,count(*) from student where gender='男' group by gender;group_concat(…) 查询同种性别中的姓名
select gender,group_concat(name) from student where gender='男' group by gender; select gender,group_concat(name,"_",age," ",id) from student where gender='男' group by gender;having 对分组后 条件再过滤 查询平均年龄超过30岁的性别，以及姓名 having avg(age)>30
select gender,group_concat(name),avg(age) from student group by gender having avg(age) > 30;查询每种性别中人数多于2个的信息
select gender,group_concat(name) from student group by gender having count(*) >2;where 与having区别： where是对原表区过滤判断 having是原表区分组后再过滤判断
