SQL '08: how to read all sku in one table not found in another table

Question

I would like to do something similar to this psuedo-SQL:

SELECT COUNT(A.SKU) 
  FROM TableA as A
 WHERE a.sku NOT IN TableB

Answer 1

Several solutions, for example with EXISTS:

SELECT COUNT(A.SKU) AS your_count
FROM TableA
WHERE NOT EXISTS(SELECT NULL
                 FROM TableB
                 WHERE B.SKU = A.SKU);

You can also use EXCEPT:

SELECT COUNT(*)
FROM (
    SELECT SKU
    FROM TableA
    EXCEPT
    SELECT SKU
    FROM TableB);

You can also use NOT IN, LEFT OUTER JOIN ... WHERE B.SKU NULL, etc.