All 7 Transactions & ACID questions
More in Transactions & ACID
What does ACID stand for, and what does each letter represent in the context of database transactions? How do you use a SAVE TRANSACTION savepoint within a larger transaction to allow partial rollback of just a portion of the work? What is the difference between an implicit and an explicit transaction in SQL Server? How do you check whether a transaction is currently active and view its properties within a session? How would you design a distributed transaction that needs to span operations across two different database servers, and what additional complexity does this introduce? How do long running transactions negatively impact overall system performance, and what strategies help avoid this problem?
Advertisement
SQL Server › Transactions & ACID

What is a transaction in SQL Server, and why is grouping multiple statements into one important?

Beginner

Answer

A transaction groups one or more SQL statements together so they are treated as a single unit of work, meaning either all of the statements succeed together and their changes are saved, or if something goes wrong, all of the changes are undone together, protecting your data from being left in an inconsistent, partially updated state.
BEGIN TRANSACTION;
UPDATE Accounts SET Balance = Balance - 100 WHERE AccountId = 1;
UPDATE Accounts SET Balance = Balance + 100 WHERE AccountId = 2;
COMMIT TRANSACTION;
Real-world example A bank transfer uses a transaction to ensure that money is either successfully moved from one account to another completely, or not moved at all if something fails, preventing money from disappearing or being duplicated.

Common follow-ups: What happens if the second statement in a transaction fails after the first one already succeeded?;What is the difference between COMMIT and ROLLBACK?

Error Handling with TRY CATCH;Isolation & Locking
All 7 Transactions & ACID questions