What's wrong with this T-SQL MERGE statement? - tsql

Question

I am new to MERGE, and I'm sure I have some error in my code.
This code will run and create my scenario:
I have two tables, one that is called TempUpsert that fills from a SqlBulkCopy operation (100s of millions of records) and a Sales table that holds the production data which is to be indexed and used.
I wish to merge the TempUpsert table with the Sales one
I am obviously doing something wrong as it fails with even the smallest example
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[TempUpsert]') )
drop table TempUpsert;
CREATE TABLE [dbo].[TempUpsert](
[FirstName] [varchar](200) NOT NULL,
[LastName] [varchar](200) NOT NULL,
[Score] [int] NOT NULL
) ON [PRIMARY] ;
CREATE TABLE [dbo].[Sales](
[FullName] [varchar](200) NOT NULL,
[LastName] [varchar](200) NOT NULL,
[FirstName] [varchar](200) NOT NULL,
[lastUpdated] [date] NOT NULL,
CONSTRAINT [PK_Sales] PRIMARY KEY CLUSTERED
(
[FullName] ASC
)
---- PROC
CREATE PROCEDURE [dbo].[sp_MoveFromTempUpsert_to_Sales]
(#HashMod int)
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
MERGE Sales AS trget
USING (
SELECT
--- Edit: Thanks to Mikal added DISTINCT
DISTINCT
FirstName, LastName , [Score], LastName+'.'+FirstName AS FullName
FROM TempUpsert AS ups) AS src (FirstName, LastName, [Score], FullName)
ON
(
src.[Score] = #hashMod
AND
trget.FullName=src.FullName
)
WHEN MATCHED
THEN
UPDATE SET trget.lastUpdated = GetDate()
WHEN NOT MATCHED
THEN INSERT ([FullName], [LastName], [FirstName], [lastUpdated])
VALUES (FullName, src.LastName, src.FirstName, GetDate())
OUTPUT $action, Inserted.*, Deleted.* ;
--print ##rowcount
END
GO
--- Insert dummie data
INSERT INTO TempUpsert (FirstName, LastName, Score)
VALUES ('John','Smith',2);
INSERT INTO TempUpsert (FirstName, LastName, Score)
VALUES ('John','Block',2);
INSERT INTO TempUpsert (FirstName, LastName, Score)
VALUES ('John','Smith',2); --make multiple on purpose
----- EXECUTE PROC
GO
DECLARE #return_value int
EXEC #return_value = [dbo].[sp_MoveFromTempUpsert_to_Sales]
#HashMod = 2
SELECT 'Return Value' = #return_value
GO
This returns:
(1 row(s) affected)
(1 row(s) affected)
(1 row(s) affected)
Msg 2627, Level 14, State 1, Procedure sp_MoveFromTempUpsert_to_Sales, Line 12
Violation of PRIMARY KEY constraint 'PK_Sales'. Cannot insert duplicate key in object
'dbo.Sales'. The statement has been terminated.
(1 row(s) affected)
What am I doing wrong please?
Greatly appreciated

Answer 1

The first two rows in your staging table will give you the duplicate PK. violation. Conc is the PK and you insert tmain+dmain with the same value twice.

Answer 2

In Summation
MERGE requires its input (Using) to be duplicates free
the Using is a regular SQL statement, so you can use Group By, distinct and having as well as Where clauses.
My final Merge looks like so :
MERGE Sales AS trget
USING (
SELECT FirstName, LastName, Score, LastName + '.' + FirstName AS FullName
FROM TempUpsert AS ups
WHERE Score = #hashMod
GROUP BY FirstName, LastName, Score, LastName + '.' + FirstName
) AS src (FirstName, LastName, [Score], FullName)
ON
(
-- src.[Score] = #hashMod
--AND
trget.FullName=src.FullName
)
WHEN MATCHED
THEN
UPDATE SET trget.lastUpdated = GetDate()
WHEN NOT MATCHED
THEN INSERT ([FullName], [LastName], [FirstName], [lastUpdated])
VALUES (FullName, src.LastName, src.FirstName, GetDate())
OUTPUT $action, Inserted.*, Deleted.* ;
--print ##rowcount
END
And it works!
Thanks to you all :)

Answer 3

Without DISTINCT or proper AGGREGATE function in subquery used in USING part of MERGE there will be two rows which suits criteria used in ON part of MERGE, which is not allowed. (Two John.Smith)
AND
Move the condition src.[Score] = #hashMod inside the subquery,
instead if ON clause not succeed, for example John.Smith have score of 2, and #HashMod = 1 - then if you already have the row with John.Smith in target table - you'll get an error with Primary Key Constraint