MySQL 8 Cookbook

Read uncommitted

The current transaction can read data written by another uncommitted transaction, which is also called dirty read.

For example, A wants to add some amount to his account and transfer it to B. Assume both the transactions happen at the same time; the flow will be like this.

A initially has $400 and wants to transfer $500 to B after adding $500 to his account.

# Transaction 1 (adding amount)	# Transaction 2 (transferring amount)
BEGIN;	BEGIN;
UPDATE account SET balance=balance+500 WHERE account_number='A';	--
--	SELECT balance INTO @a.bal FROM account WHERE account_number='A'; # A sees 900 here
ROLLBACK; # Assume due to some reason the transaction got rolled back	--
--	# A transfers 900 to B since A has ...