MERGE语法SQL Server 2012错误

Question

MERGE对我无法找到答案的语法有疑问.

我有以下情况:

步骤1:

create temp table #TempTbl

第二步MERGE:

MERGE INTO T1 target 
USING T2 AS source ON (bunch of columns)

WHEN MATCHED 
    UPDATE 
        SET some columns from target equal some columns from source

WHEN NOT MATCHED BY TARGET 
    THEN INSERT (bunch of columns) 
         VALUES (bunch of columns from SOURCE) 

OUTPUT $action, deleted.* into #TempTbl

我需要知道的是,对于我的上述步骤,我不会在临时表中找到空数据#TempTbl,正如我所说WHEN NOT MATCHED ... THEN INSERT,不是DELETE吗？

第二个问题,应该$action是什么类型的列,因为我有错误消息:

列名或提供的值与表定义不匹配

虽然我试图从我的表都定义了第一列varchar(100),nvarchar(100)但没有运气.但是,如果我省略该$action字段,那么我的陈述可行.

Answer 1

因此,将保存$ action的列应该是nvarchar(10).

以下语句将为临时表添加行insert和update(因为更新实际上是删除后跟插入)但具有不同的操作:

-- sample test data
create table t1 (col1 int, col2 int)
create table t2 (col1 int, col2 int)
insert t1 values (1,1),(2,1)
insert t2 values (2,2),(3,3)
create table #temptbl (dml_action nvarchar(10), col1 int, col2 int)

-- merge statement
merge into t1 target 
using t2 as source 
  on target.col1 = source.col1
when matched 
    then update set target.col2 = source.col2
when not matched by target 
    then insert (col1, col2) values (source.col2, source.col2) 
output $action, inserted.col1, inserted.col2 into #temptbl ;

-- sample result

select * from #temptbl

dml_action col1        col2
---------- ----------- -----------
INSERT     3           3
UPDATE     2           2

如果您不想要update行,则可以将整个批处理包装到另一个语句中,如下所示:

insert #temptbl (dml_action, col1, col2)
select dml_action, col1, col2 
from 
(
    merge into t1 target 
    using t2 as source 
     on target.col1 = source.col1
    when matched 
       then update set target.col2 = source.col2
    when not matched by target 
       then insert (col1, col2) values (source.col2, source.col2) 
    output $action as dml_action, inserted.col1, inserted.col2 
) a
where a.dml_action = 'INSERT'