- A Single unit of work
- Often made up of multiple db operations
- To provide a reliable and consistent unit of work, even in case of system failure
- to provide isolation between programs that access the database concurrently
- The database must satisfy the ACID PROPERTY
- Atomicity : Either all operations complete successfully or the transaction fails and the db is unchanged.
- Consistency : The db state must be valid after the transaction. All constraints must be satisfied.
- Isolation : Concurrent transactions must not affect each other.
- Durability : Data written by a successful transaction must be recorded in persistent storage
BEGIN; ... COMMIT;`
- if any query fails we rollback
BEGIN;...