Transaction with multiple updates and unique index

Question

Aryan Kumar · Answer

Sure, here is an example of a transaction with multiple updates and a unique index:
SQL
BEGIN TRANSACTION;
UPDATE Customers
SET FirstName = 'John',
LastName = 'Doe'
WHERE CustomerID = 1;
UPDATE Customers
SET FirstName = 'Jane',
LastName = 'Doe'
WHERE CustomerID = 2;
-- Check for unique constraint violation
IF EXISTS (
SELECT 1
FROM Customers
WHERE FirstName = 'Jane'
AND LastName = 'Doe'
)
BEGIN
ROLLBACK TRANSACTION;
END;
COMMIT TRANSACTION;
This transaction will update the Customers table to change the first and last names of the customers with the IDs 1 and 2. However, it will first check to see if there is already a customer with the first name
Jane and the last name Doe. If there is, the transaction will roll back, meaning that the updates will not be made.
The BEGIN TRANSACTION statement starts the transaction. The 
UPDATE statements update the Customers table. The IF EXISTS statement checks for a unique constraint violation. The
ROLLBACK TRANSACTION statement rolls back the transaction if there is a unique constraint violation. The
COMMIT TRANSACTION statement commits the transaction.
This code is not complete, as it does not handle errors that could occur during the transaction. However, it provides a basic example of how to perform a transaction with multiple updates and a unique index.

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Transaction with multiple updates and unique index

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