T-SQL:带有标识列的CTE

时间:2012-04-23 10:22:01

标签: sql-server-2008 common-table-expression identity-column

我正在构建一个树(物料清单样式),并转换一些数据。请考虑下表:

BillOfMaterials

  • BomId
  • 的ParentId

现在我正在使用CTE来填补它:

with BOM as 
(
select @@identity as BomId, null as ParentId <some other fields> from MyTable
union all
select @@identity as BomId, 
       parent.BomId as ParentId,
       some other fields
from MyTable2
inner join BOM parent on blabla)

insert into MyTable3
select * from BOM

问题是:@@ identity只会给我联盟之前插入的最后一条记录的身份。

我该怎么做才能获得身份?我可以修改Table3但不能修改Table1或Table2

row_number()对递归查询有未定义的行为,所以我不能在这里使用它。

我知道我可以使用GUID,这是唯一的选择吗?

2 个答案:

答案 0 :(得分:3)

您无法在CTE中捕获生成的标识。但是,您可以将所有行插入目标表,nullParentID,然后在单独的更新语句中更新ParentID。为此,您可以使用merge和描述here的技术。

-- Helper table to map new id's from source
-- against newly created id's in target
declare @IDs table
( 
  TargetID int,
  SourceID int,
  SourceParentID int
)

-- Use merge to capture generated id's
merge BillOfMaterials as T
using SourceTable as S
on 1 = 0
when not matched then
insert (SomeColumn) values(SomeColumn)
output inserted.BomId, S.BomID, S.ParentID into @IDs;

-- Update the parent id with the new id
update T
set ParentID = I2.TargetID
from BillOfMaterials as T
  inner join @IDs as I1
    on T.BomID = I1.TargetID
  inner join @IDs as I2
    on I1.SourceParentID = I2.SourceID

以下是SE-Data

上的完整工作示例

答案 1 :(得分:2)

@@identity会显示您会话的实际身份值。

您不能将CTEIDENTITY FUNCTION一起使用,但可以使用临时表:

SELECT IDENTITY(int,1,1) AS  BomId, un.*
INTO #BOM
FROM <your union> as un

如果您想使用CTE:

with BOM as 
(
  SELECT ROW_NUMBER() OVER(ORDER BY <column> ) AS  BomId, un.*
  FROM <your union> as un
)