Constructing query with a search criteria for one column based on what is found in another column.

[Nanuaraq]

I am doing a survey of agents on a particular market.


I have comprehensive data about who delivers to who. Several of the receivers may also act as suppliers to others. Like, agent A delivers to agent C, agent B delivers to agent C, agent C delivers to agent D, and so on.
They are in a table like this:
Supplier.Receiver
A..........C
B..........C
C..........D

I am trying to find out which of the receivers that do not act as supplier to anyone else. In the example above, I am looking for D because D is not anywhere in the column "Supplier". I am neither looking for A, B nor C.
D has the characteristic that it is not found in the column "Supplier" and so it ought to be possible to do a query that shows me this extract of the table above:
Supplier.Receiver
C..........D

How to do?
Thank you in advance.

[June7]

Consider:

SELECT Table1_1.Supplier, Table1_1.Receiver
FROM Table1 AS Table1_1 LEFT JOIN Table1 ON Table1_1.Receiver = Table1.Supplier
WHERE (((Table1.Supplier) Is Null));

[Nanuaraq]

Consider:

SELECT Table1_1.Supplier, Table1_1.Receiver
FROM Table1 AS Table1_1 LEFT JOIN Table1 ON Table1_1.Receiver = Table1.Supplier
WHERE (((Table1.Supplier) Is Null));

Boy, I have no idea how this worked, but it did!
Thank you, this came in handy.

Ultimately, it turned out the resulting picture of companies and their relations were so arbitrary that no useful data cuold be obtained, but not it's tested.