1.创建数据库
create database mytest;
2.创建表并填充数据,填充方式有手动填充以及导入数据user,item,action
create table user{
  user_id
  user_sex
  user_birthday
  user_terms
 }
 3.数据说明 
 表 user:        字段  user_id,user_sex,user_birthday,user_terms
 表 item:        字段  item_id,item_cat,item_terms
 表 action:      字段  user_id,item_id,creat_at,action

 use mytest;
 status
展现数据
DESC user;
select * from  user limit 3;

1.只排一列
select user_birthday from user order by user_birthday;
select user_birthday from user order by user_birthday;  
DESC;

2.多列排序,升序ASC是默认的
select * from user order by user_id,user_birthday;
select * from user order by user_id DESC,user_birthday;
select * from user order by user_id ,user_birthday DESC;
select * from user order by user_id DESC,user_birthday    DESC;

按照自定义列排序

在SQL中,会中表内容的数据,使用分组来查询
select user_sex ,count(*) from user group by user_sex；