mysql leftjoin ,一对多,如何关联到右表最新的记录 - V2EX
wq67200976

mysql leftjoin ,一对多,如何关联到右表最新的记录

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  •   wq67200976 Sep 19, 2020 2309 views
    This topic created in 2067 days ago, the information mentioned may be changed or developed.
    假设有数据表 user, user_login,
    user 表,
    id | uid
    1 | 1001
    2 |002

    user_login 表

    id | uid | content

    1 | 1001 | 数据 1 |
    2 | 1002 | 数据 2 |
    3 | 1001 | 数据 3|
    4 | 1001 | 数据 4 |
    5 | 1002 | 数据 5|

    现在将 user 表当主表,左连接查询 login 表,
    select * from user as t1 left join (select max(id),content group by uid)
    这样查到的结果 uid 和 content 对不上,也就是会随机选择一个值,

    像这种情况想要根据主表的 uid,不同的 uid 匹配关联表中 uid 相等的最新一条记录该如何做。

    这个表字段等都是随手写的,不用考虑太多,像这种能不能通过只通过 sql 语句查出来
    yungo8
        1
    yungo8  
       Sep 19, 2020 via Android
    右表建议再包装一层查 maxID 记录的 content 。

    不知道我印象中有问题还是新的特性啥的,我之前用 group by,结果中只能是 group by 后的字段加聚合函数之类的
    flgn88
        2
    flgn88  
       Sep 19, 2020 via iPhone
    可以先用 group by 处理 login 表拿到每个 uid 的最新 id 的 record,然后插回 user 表吧,应该就没有多对一插入这种随机问题性了。
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