What is Transaction? Why we need transaction in Sql Server

A transaction is a unit of work which must be made permanent as a whole must be undone is a whole. Transactions are consists of one or more DML operations. This property is called Automocity.

               In SQL Server the transactions can be control by using commit and Rollback command. Sql server runs in following transaction modes

1.      Auto Commit Mode

2.      Implicit transaction Mode

3.      Explicit transaction Mode