mysql分组和排序操作

mysql分组和排序操作
分组、排序操作

select * from student order by id desc,height asc; 排序,mysql默认根据主键正序排列,order by 排序字段,asc正序,desc倒序,防止一个条件相同内容导致无法排序,再增加第二个排序条件进行排序

select count(*),gender from student group by gender; group by分组,以gender分组,select与from之间为打印出来的内容,分别统计男、女人数

select count(*),age from student where age = 20 group by age; 打印student表格里年龄为20的人数

select count(*),age,group_concat(id) from student where age = 20 group by age;

select gender,count() from student group by gender having count() > 3; student表格里以gender分组,打印gender与count个数,having必须跟group by使用,是在分组后二次筛选

select * from student limit 1,2; limit限制 1:从第二个开始,取2个数据

select * from student order by rand() limit 1,2; order by rand()随机取数据

select gender,count(*) from student group by gender with rollup; 以gender分组,gender和count, with rollup累加count

转自：https://www.cnblogs.com/sunzhiqi/p/10072692.html