Using SQL MERGE with vars instead of a table - sql

Question

take the following table (a very simplified example):
CREATE TABLE [dbo].[tbl_Order_Lines] (
[LineID] [int] IDENTITY(1, 1) NOT NULL ,
[OrderID] [int] NOT NULL ,
[StockCode] [varchar](20) NOT NULL ,
[Quantity] [smallint] NOT NULL
)
I have a proc that controls insertions into this table, but at one point you come to the infamous "UPSERT" scenario.
Let’s assume my procedure has the following vars:
#OrderID INT ,
#StockCode VARCHAR(20) ,
#Quantity SMALLINT
I currently do as follows:
IF ( NOT EXISTS ( SELECT *
FROM [dbo].[tbl_Order_Lines]
WHERE [OrderID] = #OrderID
AND [StockCode] = #StockCode )
)
INSERT INTO [dbo].[tbl_Order_Lines]
( [OrderID] ,
[StockCode] ,
[Quantity]
)
VALUES ( #OrderID ,
#StockCode ,
#Quantity
)
ELSE
UPDATE [dbo].[tbl_Order_Lines]
SET Quantity = #Quantity
WHERE [OrderID] = #OrderID
AND [StockCode] = #StockCode
My intention is to do away with this old method and use the MERGE statement - however i'm struggling to get my head round the MERGE statement, this is what i have so far:
MERGE dbo.tbl_Order_Lines
USING (
VALUES
( #Quantity
) ) AS Source ( Quantity )
ON dbo.tbl_Order_Lines.OrderID = #OrderID AND StockCode = #StockCode
WHEN MATCHED THEN
UPDATE SET Quantity = source.Quantity
WHEN NOT MATCHED THEN
INSERT (
OrderID ,
StockCode ,
Quantity
) VALUES
( #OrderID ,
#StockCode ,
Source.Quantity
);
My Question(s):
My attempt at this MERGE seems to work - yet it looks VERY messy and confusing - is there a better way of writing this?
How would i modify this MERGE statement to DELETE matching rows (based on OrderID & StockCode) if #Quantity = 0

Answer 1

You could tighten up the last part by using the special $action keyword.
Case $action
When 'INSERT' Then 'OK_ADDED'
When 'UPDATE' Then 'OK_UPDATED'
When 'DELETE' Then 'OK_REMOVED'
End
$action
Is available only for the MERGE statement. Specifies a column of type nvarchar(10) in the OUTPUT clause in a MERGE statement that returns one of three values for each row: 'INSERT', 'UPDATE', or 'DELETE', according to the action that was performed on that row.
Output Clause.

Answer 2

OK, this is what i came up with:
MERGE dbo.tbl_Order_Lines
USING ( VALUES ( #Quantity ) ) AS Source ( Quantity )
ON dbo.tbl_Order_Lines.OrderID = #OrderID AND StockCode = #StockCode
WHEN MATCHED AND #Quantity > 0 THEN
UPDATE SET Quantity = source.Quantity
WHEN MATCHED AND #Quantity <= 0 THEN
DELETE
WHEN NOT MATCHED AND #Quantity > 0 THEN
INSERT (
OrderID ,
StockCode ,
Quantity
)
VALUES
( #OrderID ,
#StockCode ,
Source.Quantity
)
OUTPUT
COALESCE(Inserted.LineID, Deleted.LineID) AS ResultID ,
CASE WHEN Deleted.LineID IS NULL
AND Inserted.LineID IS NOT NULL THEN 'OK_ADDED'
WHEN Deleted.LineID IS NOT NULL
AND Inserted.LineID IS NOT NULL THEN 'OK_UPDATED'
WHEN Deleted.LineID IS NOT NULL
AND Inserted.LineID IS NULL THEN 'OK_REMOVED'
END AS ResultDesc
INTO #tbl_LineChanges ( ResultID, ResultDesc );
Would still love to know if there is a tider way of writing this!