database atomicity consistency

Question

What is difference between Atomicity and consistency ? it looks to me as both are saying same thing in different word.

Atomicity

All tasks of a transaction are performed or none of them are. There are no partial transactions. For example, if a transaction starts updating 100 rows, but the system fails after 20 updates, then the database rolls back the changes to these 20 rows.

Consistency

The transaction takes the database from one consistent state to another consistent state. For example, in a banking transaction that debits a savings account and credits a checking account, a failure must not cause the database to credit only one account, which would lead to inconsistent data.

and looks like atomicity is subset of consistency, then it shoud be cid(conistency, isolation, duribility) ,no atomicity

Answer 1

Atomicity is indeed saying that each transaction is either all or nothing, meaning that either all or none of its actions are executed and that there are no partial operations.

However, consistency talks about ensuring that any transaction will bring the database from one valid state to another. Any data written to the database must be valid according to all defined rules, including but not limited to constraints, cascades, triggers, and any combination thereof (taken from Wikipedia). That basically means that only valid states are written to the database, and that a transaction will either be executed if it doesn't violate the data consistency or rolled back if it does.

Hope it clears things out for you.