使用 DISTINCT 內連接 SQL

Question

我有兩張桌子 T1 和 T2 我的桌子看起來像這樣

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

T2 上的 UserKey 與 CommenterKey 相關

我想加入這兩個表，同時根據每個唯一的 AppKey 過濾評論列上的重復評論

任何關於如何使這項工作的想法將不勝感激。

這是示例數據：

這里的想法是過濾與某個 appkey 有關的重復評論，如果您查看 Appkey 列中的第 11-15 行它是相同的 appkey 如果您查看第 11-15 行它是相同的評論我想過濾這些評論out 所以查詢不會返回這些重復的行。

下面是我使用的查詢

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

您的示例數據很難閱讀。 但是，您可以使用row_number()或聚合。 我認為這可以滿足您的要求：

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 2

根據示例數據，這樣的事情應該可以工作。

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

您最大的問題可能是性能。 您可能需要考慮添加重復標志並通過觸發器或計划作業進行檢查。

Answer 3

您還可以使用 CTE 表。 下面的鏈接是關於 CTE 表和如何使用它的介紹

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

我認為這可以滿足您的要求，

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;