Nested Transaction in SQL Server

Transaction: Transaction is the collection of T-SQL statements which executes in single unit. Transaction begins with a specific T-SQL statement and ends when all T-SQL statements execute successfully. If any statements fail then transaction fails. Transaction has only two types of results success or failed. For more detail, what is Transaction inSQL Server?

Nested Transaction:  Microsoft SQL Server allows starting transaction within transaction which is called Nested Transaction. Nested transaction can be COMMIT but can’t be ROLLBACK.

See Following Example:

CREATE TABLE Employee (             ID INT PRIMARY KEY,             Name VARCHAR(50),             Emp_Address VARCHAR(100) )

Run above script to create an Employee table where ID column is PRIMARY KEY. Now see following script.

BEGIN             BEGIN TRY                         BEGIN TRANSACTION OUT1                                     INSERT INTO Employee VALUES(1,'DILIP','NOIDA')                                                       BEGIN TRANSACTION INNER1                                     INSERT INTO Employee VALUES(1,'RAJ','DELHI')                                              COMMIT TRANSACTION                         END TRY             BEGIN CATCH                   ROLLBACK TRANSACTION INNER1             END CATCH END

This script will generate an error “Cannot roll back INNER1. No transaction or savepoint of that name was found.”

Employee has “ID” PRIMARY KEY column in both transactions we trying to insert same value 1 so our transaction failed. In CATCH block we trying to ROLLBACK to INNER1 transaction so above we got an error.

If we are trying to rollback to OUT1 transaction it will run without error.

See following script

BEGIN             BEGIN TRY                         BEGIN TRANSACTION OUT1                                     INSERT INTO Employee VALUES(1,'DILIP','NOIDA')                                                       BEGIN TRANSACTION INNER1                                     INSERT INTO Employee VALUES(1,'RAJ','DELHI')                                              COMMIT TRANSACTION                         END TRY             BEGIN CATCH             ROLLBACK TRANSACTION OUT1             END CATCH END

Note: Here SQL server allow to rollback only outer transaction and rollback of outer transaction will rollback all inner transaction.

Using Save transaction we can perform partial rollback in transaction

Using SAVE TRANSACTION command we can perform partial rollback, see following script

BEGIN TRANSACTION INSERT INTO Employee VALUES(1,'DILIP','NOIDA')       --Save transaction Command SAVE TRANSACTION INNER1 INSERT INTO Employee VALUES(2,'RAJ','DELHI')          SELECT * FROM Employee ROLLBACK TRANSACTION INNER1 COMMIT SELECT * FROM Employee

Here will find only one record in table after final commit.