Read uncommitted Table Hint in SQL Server

The Read uncommitted table hint allows a query to read data that has been modify by other transaction but not yet committed. It means it will return dirty reads which can lead to inconsistent data. This is equivalent to using the SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED statement of session level.

It is similar to nolock table hint. This hint is similar to NOLOCK. It specifies that the Database Engine not issue shared locks and not honor exclusive locks. When this option is set, it is possible to read uncommitted or dirty data; values in the data can be changed and rows can appear or disappear in the data set before the end of the transaction.

See the example as below

We have a table

Now in one session we are updating this table and not yet committed.

begin tran   update Employees set Department='ADMIN' where EmployeeID=5   --commit

This transaction is not yet committed. Now we are selecting this table on anther window let’s see

Still this is running.

Now we are using this table hint.

select * from Employees WITH (READUNCOMMITTED) where EmployeeID=5

Here we are getting the un committed data. This is similar to NOLOCK hint.