合并语句中的删除语句问题

Question

我正在使用 merge into 语句

我有一个 table 看起来像这样（首先我像这样插入）使用下面的查询：


5	2
5	3
5	5
5	6

table 输入：

CREATE TYPE [dbo].[userid] AS TABLE(
    [userid] [bigint] NULL
)
GO

现在我想要以下输出：


5	2
5	3
5	6

我这样写下面的查询：

--use test
declare @sid varchar(100) = '5'
declare @uid as userid

insert into @uid(userid) values(2)
insert into @uid(userid) values(3)
--insert into @uid(userid) values(5)    // I remove this line 
insert into @uid(userid) values(6)

MERGE INTO dbo.test_master AS dest
USING @uid AS sou ON
    dest.sid = @sid
    AND
    sou.userid = dest.testid
WHEN MATCHED THEN UPDATE SET
    dest.testid = sou.userid
WHEN NOT MATCHED THEN
    INSERT( sid, testid )
    VALUES( @sid, sou.userid )
--WHEN NOT MATCHED BY SOURCE
--    THEN
--        DELETE
;

我正在尝试实现此输出


5	2
5	3
5	6

我正在使用 delete 关键字，查看我的 SQL 查询，但它正在删除 table 中的所有记录。我试了，还是不行。

Answer 1

您需要预过滤目标 table，否则所有行，即使那些具有不同 sid 将被删除。您可以使用 CTE 或视图进行预过滤。

I note that the WHEN MATCHED clause makes no sense, as the only column being updated is the join column, which obviously matches anyway.

declare @sid varchar(100) = '5';
declare @uid as userid;

insert into @uid (userid) values
  (2),
  (3),
--  (5),    -- I remove this line 
  (6);

WITH dest AS (
    SELECT *
    FROM dbo.test_master dest
    WHERE dest.sid = @sid
)
MERGE INTO dest
USING @uid AS sou ON
    sou.userid = dest.testid
-- WHEN MATCHED THEN UPDATE SET
--    dest.testid = sou.userid   -- doesn't make sense
WHEN NOT MATCHED THEN
    INSERT( sid, testid )
    VALUES( @sid, sou.userid )
WHEN NOT MATCHED BY SOURCE THEN 
    DELETE
;

db<>fiddle

合并语句中的删除语句问题

Issue with delete statement in merge statement

sql-server

merge