Insert Data if not exists (from 2 tables) and Update otherwise - sql

Question

Good day. I have 3 tables:
tblWarehouseProducts:
ProductID
ProductName
ProductCode
Quantity
tblBranchProducts:
ProductID
ProductCode
ProductCode
Quantity
Location
tblStockMoves:
ProductID
DestinationLocation
Quantity
ReferenceNumber
Basically, the process is that Branch X requests a product from Warehouse Y. Warehouse Y then creates a request order(called a Stock Move) and stores the request in tblStockMove.
Say for this case, we have a Stock Move with Reference Number XYZ:
REFERENCE NO. | PRODUCT ID | DESTINATION | QTY |
XYZ | 1 | BRANCH Y | 5 |
XYZ | 2 | BRANCH Y | 6 |
(where ProductID 1 is Coke and ProductID 2 is Pepsi.) Branch X on the other hand has this product on stock:
PRODUCT ID | PRODUCT NAME | PRODUCT CODE | QUANTITY | LOCATION |
1 | COKE | ABC123 | 6 | Branch X |
I am currently trying to check if the items from tblStockMoves exist in tblBranchProducts.
If Product 1 exists, it will add the Qty from tblStockMoves to the current Qty in tblBranchProducts. Product 2 will be added as a new entry since it is a new item.
I am using this query below but so far, all it does is update the stock of ProductID 1 while ignoring (not inserting) Product ID 2.
IF EXISTS (select ProductID, Location
from tblBranchProducts a
where Location = 'Branch X'
and a.ProductID in (select b.ProductID
from tblStockMoves b
where b.ReferenceNumber = 'XYZ'
and b.DestinationLocation = 'Branch X'))
BEGIN
UPDATE tblBranchProducts
SET Quantity = a.Quantity + b.Quantity
FROM tblBranchProducts a
INNER JOIN tblStockMoves b ON a.ProductID = b.ProductID
WHERE
b.ReferenceNumber = 'XYZ'
AND b.DestinationLocation = 'Branch X'
END
ELSE
BEGIN
INSERT INTO tblBranchProducts (ProductID, ProductName, ProductCode, Quantity, Location)
SELECT
b.ProductID, a.ProductName, a.ProductCode, b.Quantity, b.DestinationLocation
FROM
tblStockMoves b
INNER JOIN
tblWarehouseProducts a ON b.ProductID = a.ProductID
WHERE
b.ReferenceNumber = 'XYZ'
AND b.DestinationLocation = 'Branch X'
Other details such as Product Name and Product Code are pulled from tblWarehouseProducts and then inserted to tblBranchProducts.
Can anyone tell me why my query only updates the existing stock of Product 1 and not inserting Product 2?
Your answers are deeply appreciated!

Answer 1

You can do it dynamically for all products with out IF's , just addthe conditions required:
/*will insert all the unmatched products*/
INSERT INTO tblBranchProducts (ProductID, ProductName, ProductCode, Quantity, Location)
SELECT b.ProductID, a.ProductName, a.ProductCode, b.Quantity, b.DestinationLocation
FROM tblStockMoves b
inner join tblWarehouseProducts a on b.ProductID = a.ProductID
LEFT JOIN tblBranchProducts c ON(a.productid = b.productid)
where c.productid is null
And:
/*will update all the matching products*/
update tblBranchProducts a
INNER join tblStockMoves b on a.productid = b.productid
set a.quantity= b.qty