What is a transaction?

Treat several operations as one unit.

What is a transaction?

A transaction is one or more operations treated as a single unit. All or nothing.

BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT;

A money transfer is one unit.

What is a transaction? — details

A transaction either fully succeeds or does not happen. On error it is rolled back with ROLLBACK.

For example, in a money transfer, debiting one account and crediting another is one transaction; if the second step fails, the first is undone and no money is lost.

Exercise What is a transaction?

Start a transaction: write two UPDATEs with BEGIN and COMMIT.

Show example solution

BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT;

Test yourself

What is the transaction principle?
- No going back
- Partial success
- All or nothing
- Automatic saving
Show answer

All or nothing — A transaction is all or nothing.

Add BEGIN

____;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
COMMIT;

Show answer

BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
COMMIT;

What is a transaction: match the terms

transaction

transaction
BEGIN

start
COMMIT

commit
ROLLBACK

rollback

Next lesson: BEGIN and COMMIT

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