query to dispaly from two tables with negation

Question

I have two listboxes,listbox1 and listbox2, and two tables in a DB, table1 and table2. Both tables contain a column called 'Colour'. I want to display all 'Colours' from table1 in listbox1 which I'm able to do. But in listbox2 I want to display 'Colours' from Table2 but it must not be present in the Table1 'Colours'. So how do I write a query for it?

This is what I have been trying and its not working:

SELECT Table2.Colour
FROM Table1 CROSS JOIN Table2
WHERE  (Tabel1.Colour! = Table2.colour)

Error Message is — multi-part identifier Tabel2.Colour could not be found

Answer 1

This should work with a LEFT JOIN :

SELECT Table2.Colour 
FROM Table2 
   LEFT JOIN Table1 ON Tabel1.Colour = Table2.colour
WHERE Table1.Colour IS NULL

You could also use NOT IN or NOT EXISTS , I just prefer the LEFT JOIN / IS NULL syntax.

For example:

SELECT Colour 
FROM Table2 
WHERE Colour NOT IN (SELECT Colour FROM Table1)

Answer 2

If your version of RDBMS implements EXCEPT clause, you can do the following:

SELECT Colour FROM Table2
EXCEPT 
SELECT Colour FROM Table1

I'm not saying that this is better than JOIN. Just another option.