SQL Server: statement in a batch all execute as one transaction? - sql-server

Question

So I ran a SQL batch with a bunch of UPDATE statements:
UPDATE...;
UPDATE...;
UPDATE...;
Turns out the batch ran as a single transactions consequently many locks were created (our database monitoring software clearly shows that it was one big transaction) so apparently its similar to me writing BEGIN...COMMIT around the batch:
BEGIN TRANS;
UPDATE...;
UPDATE...;
UPDATE...;
COMMIT;
Is that really the case? Are batches always executed as one transaction? (I am not in 'explicit transaction' mode) and why is that, and can it be configured or is that just the behavior of SQL Server?
Would it change anything if I wrap every statement in a BEGIN..COMMIT, something like:
BEGIN TRANS;
UPDATE...;
COMMIT;
BEGIN TRANS;
UPDATE...;
COMMIT;
BEGIN TRANS;
UPDATE...;
COMMIT;
Thank You!

Answer 1

Assuming that you are executing your UPDATEs from a SSMS Query Window, you can refactor your code to
BEGIN TRANS;
UPDATE...;
GO
UPDATE...;
GO
UPDATE...;
GO
COMMIT;
GO WILL make each UPDATE execute prior in its own batch in the order called, but won't be committed until the final COMMIT is called.
I have tested this via the following example that you can run for yourself in SSMS.
SET NOCOUNT ON
GO
IF EXISTS ( SELECT * FROM sys.tables WHERE name = 'BatchTest' )
DROP TABLE dbo.BatchTest;
GO
CREATE TABLE dbo.BatchTest (
id INT IDENTITY (1,1) PRIMARY KEY NOT NULL
, col1 VARCHAR(50)
, col2 VARCHAR(50)
, col3 VARCHAR(50)
, col4 VARCHAR(50)
)
GO
DECLARE #i INT = 1;
WHILE ( #i <= 100 ) BEGIN
INSERT INTO dbo.BatchTest ( col1 ) VALUES ( 'col1_' + CAST ( #i AS VARCHAR(10) ) );
SET #i += 1;
END
GO
SELECT * FROM dbo.BatchTest ORDER BY id;
/*
-- test tran/commit --
-- manually select and execute the code below after the BatchTest has been created and populated with data --
SET NOCOUNT ON
GO
BEGIN TRAN;
UPDATE dbo.BatchTest SET col2 = 'col2_' + CAST ( id AS VARCHAR(10) );
GO
UPDATE dbo.BatchTest SET col3 = 'col3_' + CAST ( id AS VARCHAR(10) );
GO
UPDATE dbo.BatchTest SET col4 = 'col4_' + CAST ( id AS VARCHAR(10) );
GO
--COMMIT;
ROLLBACK;
SELECT * FROM dbo.BatchTest ORDER BY id;
*/
Please note the comments in the code about selecting and executing the tran/commit test.
The single ROLLBACK undoes all of the UPDATEs within the current transaction, regardless of the use of GOs, whereas COMMIT will commit them all. Obviously, you should do more your diligence and test against your data, but this might help with your locking issues.
Some follow-up reading in regard to SQL Server's use of GO and its intentions:
https://learn.microsoft.com/en-us/sql/t-sql/language-elements/sql-server-utilities-statements-go?view=sql-server-2017