A transaction consists of a sequence of query and/or update statements. It is a ‘unit’ of work.
The SQL standard specifies that a transaction begins implicitly when an SQL statement is executed.
The transaction must end with one of the following statements:
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Commit work
The updates performed by the transaction become permanent in the database.
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Rollback work
All the updates performed by the SQL statements in the transaction are undone.
The database provides an abstraction of a transaction as being atomic, that is, indivisible. Either all the effects of the transaction are reflected in the database, or none are (after rollback).