错误写法，having time = max(time)在分组之后执行，查询出来只有一条满足条件的数据。having过滤的是组，在order by之后执行

select id,userId,userFlag,lontitude,latitude,time,addr,locationdescribe        from user_position        group by userId        having time = max(time)        and userId in (select id from users where group_code=(select group_code from users where id = #{userId}))        ORDER BY time desc

数据格式

详细步骤

1.查询出分组的所有按时间降序的记录id并拼接

--查询出分组的所有按时间降序的记录id并拼接select group_concat(id order by `time` desc) from user_position group by userId

结果

2.查询每个分组中时间最新的那条记录的id

--查询每个分组中时间最新的那条记录的idselect SUBSTRING_INDEX(group_concat(id order by `time` desc),',',1) from user_position group by userId

结果

3.所有成员最新一条记录

select * from user_position as t where t.id in (select SUBSTRING_INDEX(group_concat(id order by `time` desc),',',1) from user_position  group by userId)

4.根据id所在组查询组成员最新数据

select * from user_position as t where t.id in (select SUBSTRING_INDEX(group_concat(id order by `time` desc),',',1) from user_position  where userId in (select id from users where group_code=(select group_code from users where id = 'qyid1')) group by userId)

结果

 

巨坑

分组不是取数据的第一条！！！

select * from user_position as u

查询结果

select * from user_position as u group by u.userId

分组后，确实取的第一条

但是！！！

select * from (select * from user_position order by userId,time desc) as u group by u.userId

网上这种先排序再分组的，结果和上面一样！！！并没有取第一条！！！

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