分组查询一定时间段的一组数据 并且需要获取最近的一条数据
使用
SUBSTRING_INDEX
GROUP_CONCAT 默认 , 链接 可以用SEPARATOR 进行字符定义
GROUP_CONCAT(created_at ORDER BY created_at DESC
SEPARATOR ‘-‘
) 对应的截取字符串时 也要相应修改
GROUP是组，CONCAT合并多个字符串,它的功能是：将group by产生的同一个分组中的值连接起来，返回一个字符串结果
SUBSTRING_INDEX 截取字符串有效位数
select count(uid) as num, id,eid,created_at,uid,
GROUP_CONCAT(created_at ORDER BY created_at DESC) AS created_at from ds_ask_person
where eid=:eid and created_at >= :start and created_at <= :end group by uid order by created_at desc limit :offset,:limit
select count(uid) as num, id,eid,created_at,uid,
SUBSTRING_INDEX(GROUP_CONCAT(created_at ORDER BY created_at DESC),‘,‘,1) AS created_at from ds_ask_person
where eid=:eid and created_at >= :start and created_at <= :end group by uid order by created_at desc limit :offset,:limit
可参考 https://blog.csdn.net/lvoelife/article/details/81781802
分组排序 SUBSTRING_INDEX--------GROUP_CONCAT
原文：https://www.cnblogs.com/JdsyJ/p/10521810.html