Question

My test table:

CREATE TABLE [dbo].[Personel](
    [PersonelID] [int] NOT NULL,
    [Name] [nchar](10) NULL,
 CONSTRAINT [PK_Personel] PRIMARY KEY CLUSTERED 
(
    [PersonelID] ASC
)
)

My Test Data:

insert into Personel
values (1, 'Jack')
, (2, 'John')
, (3, 'Kevin')

Connection A:

begin tran
update Personel
set Name = 'Michael'
where PersonelID = 1

Connection B:

SET TRANSACTION ISOLATION LEVEL ????

SELECT Name 
FROM Personel WITH (????)
where PersonelID = 1

Connection A starts a transaction and is trying to update data, but transaction is still going on. Connection B tries to read the data that is being updated.

Is there a way (an Isolation Level or a hint or combination of these two) to see the original data (Jack, not Michael) before the transaction is committed or rolled back?

Answer 1

You can access the old version of the data in the SNAPSHOT isolation level.

This requires that the database has snapshot isolation enabled before you start:

ALTER DATABASE <dbname> SET ALLOW_SNAPSHOT_ISOLATION ON

Then in connection B

SET TRANSACTION ISOLATION LEVEL SNAPSHOT

select * from Personel

There are some performance considerations with snapshot isolation, because it duplicates the rows read into tempdb.

Documentation reference