Transactions : A transaction is a set of sql statements that are executed as single sql statement,If the statement executes successfully Commit the transaction else Rollbacks on failure.
Usage :
Begin tran
insert into dbo.sampletable values('',null,GETDATE(),null)
insert into dbo.sampletable values(1,'',null,GETDATE(),null) //Inserting identity value will fail the query.
IF @@ERROR<>0
ROLLBACK
ELSE
COMMIT
In the above code,i am making an insert into an identity column which will fail the query and in turn roll back the transaction and also make a note that none of the rows would be inserted since transaction failed.
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