You can't test your SQL properly, because your table doesn't contain the right records. I added a new record to the table so that both CID and MID are both NULL. I selected them using the below query and it worked fine.

use tempdb;

GO

--Create Test Table

CREATE TABLE [dbo].[Null_Table](

[CID] [int] NULL,

[MID] [int] NULL

) ON [PRIMARY];

GO -- execute the create table batch.

--Insert Sample Data --- note the semicolons!

insert into Null_Table(CID,MID)

valueS (123,456);

insert into Null_Table(CID,MID)

valueS (123,Null);

insert into Null_Table(CID,MID)

valueS (123,0);

INSERT INTO NULL_TABLE(CID,MID) VALUES (Null, Null);

-- return all records where both CID and MID are null

SELECT *

FROM dbo.Null_Table

WHERE CID IS NULL

AND MID IS NULL;