Question

The Situation:
I am inserting information from one table to another, a source and target. When the information is inserted into the target, a primary key is created. (In this case it is an integer.) I then need to be able to tie back to the source table. However, based on the data being moved, I am not able to reliably get the 1:1 match between the target and source tables.

The Question:
Is there a way to copy the primary key that was created for record(x) in the target table and copy it as a foreign key to that same record(x) in the source table as the bulk insert is happening?

Details:
I am trying to get this done in SQL. I have a work-around to this problem but I figure there has to be a way to do what I’m asking.

Answer 1

I found my answer after reading this great article.

http://sqlblog.com/blogs/adam_machanic/archive/2009/08/24/dr-output-or-how-i-learned-to-stop-worrying-and-love-the-merge.aspx

I acheived what I was looking for by using a MERGE and its OUTPUT clause. Here is my sample code that I used to figure this out.

I started by creating 3 temporary tables, #Temp2, #Temp3 and #Temp4. #Temp2 is considered the source table. #Temp3 would be the target table and #Temp4 is a bridge. I then inserted a few rows of very simple data, in this case just one field – Value.

CREATE TABLE #Temp2(
OldID INT IDENTITY(1,1),
Value INT,
NewFK INT)

CREATE TABLE #Temp3(
NewerID INT IDENTITY(1,1),
Value INT)

CREATE TABLE #Temp4(
OldID INT NOT NULL,
NewerID INT NOT NULL,
Value INT)

INSERT INTO #Temp2(Value)
VALUES(30), (40), (50), (70)

INSERT INTO #Temp3(Value)
VALUES (333), (444), (555), (777)

Then comes the MERGE statement that does the dirty work. It will be taking the value from #Temp2 and putting it into #Temp3. It will then take the ID created in #Temp3, the ID from #Temp2 and the Value that was passed, and throw them all into #Temp4.

MERGE INTO #Temp3 AS tgt
USING #Temp2 AS src
ON 1=0
WHEN NOT MATCHED THEN
    INSERT(
    Value)
    VALUES(
    src.Value)
OUTPUT
    src.OldID,
    INSERTED.NewerID,
    src.Value
INTO #Temp4(OldID, NewerID, Value);

Then I ran an UPDATE to the staging table #Temp2 to update the NewFK field with the new ID. Lastly, do a simple SELECT to see the updated information.

UPDATE X
SET X.NewFK = Z.NewerID
FROM #Temp2 X
JOIN #Temp4 Z
ON X.OldID = Z.OldID

SELECT * FROM #Temp2

This acheived exactly what I needed and is a pretty streamlined way of doing things. I hope this will help some people who come across this question. Thanks everyone for your insight and responses.

NOTE:
I believe MERGE was introduced in SQL Server 2008.

Jonathan