基于多列删除重复项

Question

我使用以下列出了重复项：

select s.MessageId, t.* 
from Message s
join (
    select ToUserId, FromUserId, count(*) as qty
    from Message
    group by ToUserId, FromUserId
    having count(*) > 1
) t on s.ToUserId = t.ToUserId and s.FromUserId = t.FromUserId

现在，我该如何删除除一条消息以外的所有消息（我正在尝试删除重复项，以便我可以在 FromUserId and ToUserId 上应用唯一索引）。

Answer 1

使用 cte 并分配行号，以便可以删除重复对中除一个以外的所有行。

with rownums as 
(select m.*, 
 row_number() over(partition by ToUserId, FromUserId order by ToUserId, FromUserId) as rnum
 from Message m)
delete r
from rownums r
where rnum > 1

Answer 2

制作样本数据

    DECLARE @Message TABLE(ID INT ,ToUserId varchar(100),FromUserId varchar(100))
    INSERT INTO @Message(ID,ToUserId, FromUserId )
    VALUES  ( 1,'abc',  'def'  ), ( 2,'abc',  'def'  ), ( 3,'abc',  'def'  ), ( 4,'qaz',  'xsw'  )

--做删除数据

    DELETE m FROM @Message AS m 
    INNER JOIN (
         SELECT *,row_number()OVER(PARTITION BY ToUserId,FromUserId ORDER BY ID ) AS rn FROM @Message AS m
    ) t ON t.ID=m.ID
    WHERE t.rn>1

    SELECT * FROM @Message

----------- ---------- ----------
1           abc        def
4           qaz        xsw

如果没有指定行作为ID的列，可以尝试使用行地址（例如%%lockres%%）

    DELETE m FROM @Message AS m 
    INNER JOIN (
        SELECT *,row_number()OVER(PARTITION BY ToUserId,FromUserId ORDER BY %%lockres%% ) AS rn FROM @Message AS m
    ) t ON t.ID=m.ID
    WHERE t.rn>1

    SELECT *, %%lockres%% FROM @Message

基于多列删除重复项

Deleting duplicates based on multiple columns

sql

sql-server

ssms