What is a lock?

Queue concurrent access.

A lock controls concurrent access. Two operations cannot write the same resource simultaneously.

SELECT * FROM accounts WHERE id = 1 FOR UPDATE;

This query locks the row.

All columns are selected from accounts. WHERE keeps only the rows where id = 1 FOR UPDATE holds.

What is a lock? — details

Locks ensure data consistency. But excessive locking reduces performance.

For example, when two people buy the last item at the same moment, a lock prevents the stock from being decreased twice.

Lock the id=1 row in accounts with FOR UPDATE.

Show example solution

SELECT * FROM accounts WHERE id = 1 FOR UPDATE;

Add FOR UPDATE

SELECT * FROM accounts WHERE id = 1 ____

Show answer

SELECT * FROM accounts WHERE id = 1 FOR UPDATE