php - MySQL怎样查询所有用户最新的一条信息？

Question

想到用group by 但它只能显示第一条，而不能显示最新一条，
想加个order by time desc,可是orber by只能加在group by后面。

有什么办法可以查询出group by的分组中，每组内的排序中最大或最小的一行数据？

Answer 1

方案一: 通过同表子查询或联查找到最大的数据ID

select * from track where id in(select max(id)  from track group by target_id);

or

select * from track where id in(select substring_index(group_concat(id order by id desc),',',1) as maxid from track group by target_id);

方案二：分两步查询,php中先查询最大ID,再通过ID数组查询列表数据

Answer 2

select a.* from(select max(id) as id from info group by userid) b left join info a on a.id=b.id

Answer 3

把查询结果存起来，再取

Answer 4

使用order by

Answer 5

select * from ( 
    select (@mycnt := @mycnt + 1) as ROWNUM,name,age
    from tb where AGe < 20 order by name,age 
) as A where ROWNUM = 1

只懂SqlServer,这个是仿照SqlServer写法的，可以试试

Answer 6

SELECT a.id, a.user_id, a.info, a.create_time
    FROM (SELECT id, user_id, info, create_time FROM tbl_user 
        ORDER BY user_id, create_time DESC, id DESC) a
    GROUP BY a.user_id