使用 DISTINCT 内连接 SQL

Question

我有两个表 T1 和 T2 我的表看起来像这样

T1 [ID, AppKey, CommenterKey, Comment, NoteTime]
T2 [ID, UserKey, Firstname, Lastname]

在 T2 上 UserKey 与 CommenterKey 相关

我想加入这两个表，同时根据每个唯一的 AppKey 过滤评论列上的重复评论

任何关于如何使这项工作的想法将不胜感激。

这是示例数据：

这里的想法是过滤与某个 appkey 相关的重复评论如果你查看 Appkey 列中的第 11-15 行它是相同的 appkey 如果你查看第 11-15 行它是相同的评论我想过滤掉这些评论，这样查询就不会 return 这些重复的行。

下面是我使用的查询

SELECT Notes.Appkey,
        Notes.CommenterKey,
        Notes.Comment,
        Notes.NoteTime,
        Users.Firstname,
        Users.Lastname
FROM tblNotes AS Notes 
inner join
tblUsers AS Users ON Commenterkey = UserKey

Answer 1

根据示例数据，类似这样的操作应该可行。

select  n.NoteKey,
        n.AppKey,
        n.CommenterKey,
        n.Comment,
        u.Firstname,
        u.Lastname
from    Notes n
cross apply (
    select  AppKey,
            CommenterKey,
            Comment,
            max(NoteTime) as NoteTime
    from    Notes n2
    where   n.AppKey        = n2.AppKey
    and     n.CommenterKey  = n2.CommenterKey
    and     n.Comment       = n2.Comment
    group by 
            n2.AppKey,
            n2.CommenterKey,
            n2.Comment
) ni 
join    Users u ON u.UserKey = n.CommenterKey
where   ni.NoteTime = n.NoteTime

您最大的问题可能是性能。您可能需要考虑添加重复标志并通过触发器或计划作业进行检查。

Answer 2

您的示例数据相当难以阅读。但是，您可以使用 row_number() 或聚合。我认为这符合您的要求：

select un.*
from (select n.Appkey, n.CommenterKey, n.Comment, n.NoteTime,
             u.Firstname, u.Lastname,
             row_number() over (partition by u.UserKey, n.Comment order by u.UserKey) as seqnum
      from tblNotes n inner join
           tblUsers u 
           on n.Commenterkey = u.UserKey
     ) un
where seqnum = 1;

Answer 3

您也可以使用 CTE Table。下面 link 是关于 CTE Table 和如何使用它的介绍

https://www.essentialsql.com/introduction-common-table-expressions-ctes/

我认为这符合您的要求，

with cte as 
(
        select notes.Appkey as appKey, notes.CommenterKey as CommenterKey, notes.Comment as Comment, notes.NoteTime as NoteTime,
             users.Firstname as Firstname, users.Lastname as Lastname,
             row_number() over (partition by users.UserKey, notes.Comment order by users.UserKey) as sequenceNo
      from tblNotes as notes inner join
           tblUsers as users 
           on notes.Commenterkey = users.UserKey
)

select * from cte where sequenceNo = 1;

使用 DISTINCT 内连接 SQL

Using DISTINCT inner join SQL

sql

sql-server

distinct