mysql获得排序依据之前发生的分组依据

我有三个表格,在这里我只向您显示相关的列

Table: groups Columns: group_id, name.

Table: groups_to_message Columns:
group_id, message_id

Table: messages Columns: message_id,
created (date)

我基本上需要找到每个组的最后一条消息,而不必显示重复的组.

我试过像这样使用group by：

SELECT m.created, g.group_id 
FROM groupss as g 
JOIN group_to_message as gm ON (g.group_id = gm.group_id) 
JOIN messages as m 
GROUP BY g.group_id 
ORDER BY m.created DESC

这将导致成功分组,但是在ORDER BY之前完成,因此第一个结果在排序之前.

任何帮助表示赞赏.

解决方法:

如果我没看错您的问题,请使用MAX().这应该为您提供每个组的最新商品

例…

SELECT MAX(m.created), g.group_id 
FROM groupss as g 
JOIN group_to_message as gm ON (g.group_id = gm.group_id) 
JOIN messages as m ON (gm.message_id = gm.message_id)
GROUP BY g.group_id 
ORDER BY m.created DESC

标签：sql-order-by,sql,mysql,group-by
来源： https://codeday.me/bug/20191209/2095655.html