5.1.1. Transaction Concepts

A transaction is a sequence of one or more SQL statements that together form a logical unit of work that must be either applied to the database in their entirety (COMMIT) or discarded completely (ROLLBACK). A transaction is ALL OR NONE; either all parts are recorded to the database or none are. This is known as the Atomic property.

The following is a classic example of a transaction.

Mary goes to the ATM to transfer $1000 from her savings account to her checking account. Her inputs become the following SQL statements.

UPDATE savings         SET Balance = Balance _ 1000
WHERE customerid  =  444;

UPDATE checking        SET Balance = Balance + 1000
WHERE customerid  =  444;

If these were done ...

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