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id select 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!!!
参考:
https://www.cnblogs.com/Alight/p/3425357.html
https://www.jb51.net/article/23969.htm
原文地址:https://www.cnblogs.com/aeolian/p/9359898.html
时间: 2024-10-12 03:00:10