Can I make this trigger shorter / better / faster? - sql-server

Question

The task itself is very basic. I have a transaction table that moves a certain quantity of a product in or out of stock. It becomes a bit more difficult knowing that a product can be composed from multiple 'base' products and only the base products may exist in stock.
My current trigger works but works like this:
Create temporary table that can combine inserted, deleted and composed products.
Add inserted non composed products to this temp table
Add inserted composed products
Subtract deleted non composed products
Subtract deleted composed products
I now have a table containing all transactions of non composed products. But i.e. with an update of a row, the same product is added twice. Once subtracting the old value and once adding the new value.
Create second temporary table for the joined non composed products
Take a sum of the products and put these into the new temp table
Merge the stock with this temp table
Again.. my trigger works fine and i'm having no performance problem (yet) but I feel i'm missing something. I bet there is someone around here with a better solution then mine.
My tables and sample data: (fiddle here)
CREATE TABLE [dbo].[Product](
[id] [int] IDENTITY(1,1) NOT NULL,
[plantId] [int] NOT NULL,
[reference] [nvarchar](50) NOT NULL,
[composed] [bit] NOT NULL DEFAULT ((0)),
[name] [nvarchar](max) NOT NULL,
[unit] [nvarchar](50) NOT NULL,
[dateUpdate] [datetime] NOT NULL DEFAULT (getdate())
);
INSERT INTO [dbo].[Product] VALUES (2, 'FILLER VULPROF 2 BR', 0, 'FILLER VULPROF 2 BR', 'ton', GETDATE());
INSERT INTO [dbo].[Product] VALUES (2, 'K 0/2GEW BR', 0, 'K 0/2GEW BR', 'ton', GETDATE());
INSERT INTO [dbo].[Product] VALUES (2, 'K 14/20 BR', 0, 'K 14/20 BR', 'ton', GETDATE());
INSERT INTO [dbo].[Product] VALUES (2, 'KWS BR 3A31', 1, 'KWS BR 3A31', 'ton', GETDATE());
CREATE TABLE [dbo].[ProductComposition](
[id] [int] IDENTITY(1,1) NOT NULL,
[productId] [int] NOT NULL,
[parentId] [int] NOT NULL, -- This is the parent product
[quantity] [float] NOT NULL,
[dateUpdate] [datetime] NOT NULL DEFAULT (getdate())
);
INSERT INTO [dbo].[ProductComposition] VALUES (1, 4, 0.001, GETDATE());
INSERT INTO [dbo].[ProductComposition] VALUES (3, 4, 0.001, GETDATE());
CREATE TABLE [dbo].[Transaction](
[id] [int] IDENTITY(1,1) NOT NULL,
[load] [bit] NOT NULL,
[plantId] [int] NOT NULL,
[vehicleId] [int] NOT NULL,
[productId] [int] NOT NULL,
[contactId] [int] NOT NULL,
[quantity] [float] NOT NULL,
[dateUpdate] [datetime] NOT NULL DEFAULT (getdate()),
[isSynched] [bit] NOT NULL CONSTRAINT [DF_Transaction_isSynched] DEFAULT ((0))
);
CREATE TABLE [dbo].[Stock](
[id] [int] IDENTITY(1,1) NOT NULL,
[plantId] [int] NOT NULL,
[productId] [int] NOT NULL,
[quantity] [float] NOT NULL,
[dateUpdate] [datetime] NOT NULL DEFAULT (getdate())
);
My Trigger:
ALTER TRIGGER [dbo].[StockCalculate]
ON [dbo].[Transaction]
AFTER INSERT, UPDATE, DELETE AS
BEGIN
-- Create temporary table
CREATE TABLE #TransactionsComposed (
[load] [bit] NOT NULL,
[plantId] [int] NOT NULL,
[productId] [int] NOT NULL,
[quantity] [float] NOT NULL
);
-- Insert basic materials
INSERT INTO #TransactionsComposed (
[load], [plantId], [productId], [quantity])
SELECT
[Inserted].[load],
[Inserted].[plantId],
[Inserted].[productId],
[Inserted].[quantity]
FROM
[Inserted]
INNER JOIN [Product] ON [Product].[id] = [Inserted].[productId]
WHERE
[Product].[composed] = 0;
-- Insert operations
INSERT INTO #TransactionsComposed (
[load], [plantId], [productId], [quantity])
SELECT
[Inserted].[load],
[Inserted].[plantId],
[ProductComposition].[productId],
([Inserted].[quantity] * [ProductComposition].[quantity])
FROM
[Inserted]
INNER JOIN [Product] ON [Product].[id] = [Inserted].[productId]
INNER JOIN [ProductComposition] ON [ProductComposition].[parentId] = [Product].[id]
WHERE
[Product].[composed] = 1;
-- Insert basic materials but ALTER it's load status.
INSERT INTO #TransactionsComposed (
[load], [plantId], [productId], [quantity])
SELECT
CASE [Deleted].[load]
WHEN 0 THEN 1
WHEN 1 THEN 0
END,
[Deleted].[plantId],
[Deleted].[productId],
[Deleted].[quantity]
FROM
[Deleted]
INNER JOIN [Product] ON [Product].[id] = [Deleted].[productId]
WHERE
[Product].[composed] = 0;
-- Insert operations but ALTER it's load status.
INSERT INTO #TransactionsComposed (
[load], [plantId], [productId], [quantity])
SELECT
CASE [Deleted].[load]
WHEN 0 THEN 1
WHEN 1 THEN 0
END,
[Deleted].[plantId],
[ProductComposition].[productId],
([Deleted].[quantity] * [ProductComposition].[quantity])
FROM
[Deleted]
INNER JOIN [Product] ON [Product].[id] = [Deleted].[productId]
INNER JOIN [ProductComposition] ON [ProductComposition].[parentId] = [Product].[id]
WHERE
[Product].[composed] = 1;
-- Prepare multiple products for merge
CREATE TABLE #TransactionsJoined (
[plantId] [int] NOT NULL,
[productId] [int] NOT NULL,
[quantity] [float] NOT NULL
);
INSERT INTO #TransactionsJoined
([plantId], [productId], [quantity])
SELECT
[plantId],
[productId],
SUM(CASE [load]
WHEN 0 THEN [quantity]
WHEN 1 THEN 0 - [quantity]
END)
FROM
#TransactionsComposed
GROUP BY [plantId], [productId]
-- Merge composed transactions into the stock
MERGE [Stock]
USING #TransactionsJoined
ON [Stock].[plantId]=#TransactionsJoined.[plantId]
AND [Stock].[productId]=#TransactionsJoined.[productId]
WHEN NOT MATCHED BY TARGET THEN
INSERT ([plantId], [productId], [quantity])
VALUES (
#TransactionsJoined.[plantId],
#TransactionsJoined.[productId],
#TransactionsJoined.[quantity])
WHEN MATCHED THEN
UPDATE SET
[Stock].[quantity] = [Stock].[quantity] + #TransactionsJoined.[quantity],
[Stock].[dateUpdate] = GETDATE();
END