Question

我有下表和一些样本数据。

Record_ID    Counter    Serial    Owner
1           0           AAA       Jack
2           1           AAA       Kevin
3           0           BBB       Jane
4           1           BBB       Wendy

根据与上述类似的数据，我试图为MySQL编写一个SQL查询，获取每Counter个Serial个值SELECT * FROM `history` his INNER JOIN(SELECT serial, Max(counter) AS MaxCount FROM `tracking` WHERE serial IN (SELECT serial FROM `history`) GROUP BY serial ORDER BY record_id DESC) q ON his.serial = q.serial AND his.counter = q.maxcount LIMIT 0, 50的记录。 我似乎遇到问题的部分是获取查询以获取最新更新的50个唯一序列号。

以下是我根据this StackOverflow question提出的查询。

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Answer 1

它看起来像一个经典的greatest-n-per-group问题，可以通过以下方式解决：

select his.Record_ID, his.Counter, his.Serial, his.Owner
from History his
inner join(
    select Serial, max(Counter) Counter
    from History
    group by Serial
) ss on his.Serial = ss.Serial and his.Counter = ss.Counter

如果要在数据集上使用特定过滤器，则应在子查询中应用所述过滤器。

另一个来源对此问题有更多解释：SQL Select only rows with Max Value on a Column

获取最新序列号的MAX记录

1 个答案: