SQL with Manoj

SQL Server by default does not ROLLBACK a Transaction if there is error anywhere in the code inside a BEGIN TRANSACTION & COMMIT TRANSACTION block. It only skips the statement that causes the error and moves ahead.

To allow a transaction to complete entirely or fail entirely you can use the TRY-CATCH feature with ROLLBACK statement or the SET XACT_ABORT statement.

By default the SET XACT_ABORT is OFF. There ar very few cases where the T-SQL statement that raised exception are rolled back and the transaction continues processing. Depending upon the severity of the error, the entire transaction may be rolled back even when SET XACT_ABORT is OFF.

But When SET XACT_ABORT is ON, if a T-SQL statement raises an exception, then the entire transaction is terminated and rolled back.

–> Here let’s check how we can use XACT_ABORT with an example:

-- Create a test tabel and insert some records:
CREATE TABLE Tab (x INT NOT NULL PRIMARY KEY)

INSERT INTO Tab VALUES (1)
INSERT INTO Tab VALUES (2)
INSERT INTO Tab VALUES (3)
GO

-- =================================
-- Check with XACT_ABORT OFF option:
-- =================================
SET XACT_ABORT OFF; -- By default it is OFF

BEGIN TRANSACTION
	INSERT INTO Tab VALUES (4)
	INSERT INTO Tab VALUES (4) -- Statement fails but transaction is committed.
	INSERT INTO Tab VALUES (5)
COMMIT TRANSACTION
GO
/*
-- On message pane:

(1 row(s) affected)

Msg 2627, Level 14, State 1, Line 5
Violation of PRIMARY KEY constraint 'PK__Tab__3BD019E56991A7CB'. Cannot insert duplicate key in object 'dbo.Tab'. The duplicate key value is (4).
The statement has been terminated.

(1 row(s) affected)
*/

SELECT * FROM Tab
-- List records: 1,2,3,4,5
GO

-- ================================
-- Check with XACT_ABORT ON option:
-- ================================
SET XACT_ABORT ON

BEGIN TRANSACTION
	INSERT INTO Tab VALUES (6) -- Inserts 6, but the transaction is rollbacked in next step.
	INSERT INTO Tab VALUES (6) -- Statement fails and rollbacks the entire transaction.
	INSERT INTO Tab VALUES (7) -- Statement skipped as transaction is rollbacked at previous statement.
COMMIT TRANSACTION

SET XACT_ABORT OFF
GO
/*
-- On message pane:

(1 row(s) affected)

Msg 2627, Level 14, State 1, Line 5
Violation of PRIMARY KEY constraint 'PK__Tab__3BD019E56991A7CB'. Cannot insert duplicate key in object 'dbo.Tab'. The duplicate key value is (6).
*/

SELECT * FROM Tab
-- Still list records: 1,2,3,4,5
GO

-- Final cleanup
DROP TABLE Tab
GO

We can also use TRY-CATCH constructs that helps in handling transaction and can be used instead of XACT_ABORT statement. Check here how we can use them.