SQL server not listing records with NULL values
The reason for this is that a NULL represents an unknown value.

NULL is not LIKE anything and not NOT LIKE anything either.

Try running the following 2 statements on your system:

SELECT CASE WHEN null like '%a%' THEN 'true' ELSE 'false' END;
SELECT CASE WHEN null not like '%a%' THEN 'true' ELSE 'false' END;


That should return false for both statements.

So your query should look like this:

select * from sys.dm_exec_requests where session_id &gt; 55 
and (wait_type not like ('BROKER_RECEIVE_WAITFOR') or wait_type is null)