MSSQL effective trigger INSTEAD OF INSERT - sql-server

Question

I have a case when using instead-of-insert trigger is necessary. My colleagues and I wonder which one is more effective (memory usage, time to run, etc.).
The trigger checks whether the record exists in table, if no inserts the new row, otherwise updates existing row by its key. The primary key in this example is composite key of (DocumentId, VatRate).
The first variant is with checking whether the record already exists:
CREATE TRIGGER docvatsum_trg
ON DocumentVatSummary
INSTEAD OF INSERT
AS
BEGIN
IF EXISTS (
SELECT 1 FROM DocumentVatSummary a
JOIN inserted b ON (a.DocumentId = b.DocumentId AND a.VatRate = b.VatRate)
)
BEGIN
UPDATE DocumentVatSummary
SET
DocumentVatSummary.VatBase = i.VatBase,
DocumentVatSummary.VatTotal = i.VatTotal
FROM inserted i
WHERE
DocumentVatSummary.DocumentId = i.DocumentId AND
DocumentVatSummary.VatRate = i.VatRate
END
ELSE
BEGIN
INSERT INTO DocumentVatSummary
SELECT * FROM inserted
END
END;
The second variant tries to insert and if insert fails an update follows:
CREATE TRIGGER docvatsum_trg
ON DocumentVatSummary
INSTEAD OF INSERT
AS
BEGIN
SAVE TRANSACTION savepoint
BEGIN TRY
INSERT INTO DocumentVatSummary
SELECT * FROM inserted
END TRY
BEGIN CATCH
IF XACT_STATE() = 1
BEGIN
ROLLBACK TRAN savepoint
UPDATE DocumentVatSummary
SET
DocumentVatSummary.VatBase = i.VatBase,
DocumentVatSummary.VatTotal = i.VatTotal
FROM inserted i
WHERE
DocumentVatSummary.DocumentId = i.DocumentId AND
DocumentVatSummary.VatRate = i.VatRate
END
END CATCH
END;
Note: Rollback to savepoint is required, because of TRY-CATCH implementation in running transaction in TSQL.
Which one is better and why? If you have better solution, please share.

Answer 1

Use MERGE in your trigger as explained here:
MERGE SYNTAX
Code Example:
DECLARE #SummaryOfChanges TABLE(Change VARCHAR(20));
MERGE INTO Sales.SalesReason AS Target
USING (VALUES ('Recommendation','Other'),
('Review', 'Marketing'),
('Internet', 'Promotion'))
AS Source (NewName, NewReasonType)
ON Target.Name = Source.NewName
WHEN MATCHED THEN
UPDATE SET ReasonType = Source.NewReasonType
WHEN NOT MATCHED BY TARGET THEN
INSERT (Name, ReasonType) VALUES (NewName, NewReasonType)
OUTPUT $action INTO #SummaryOfChanges;