Question

Please review this statement:

   SELECT TableID FROM Table t1
   INNER JOIN BlackList b ON b.TableID <> t1.TableID

I was thinking this statement returned everything from Table that wasn’t found in the Blacklist table, but instead it returned nothing at all (0 rows). If I’m trying to return everything from Table that IS NOT found in the Blacklist table, what’s the best way to do this? I assume you can do this:

  SELECT TableID FROM (
    SELECT TableID, CASE WHEN b.TableID IS NULL THEN 1 ELSE 0 END OnBlackList 
    FROM Table t1
      LEFT JOIN Blacklist b ON b.TableID = t1.TableID
    ) tb1
  WHERE tb1.OnBlackList = 0

But I was looking for a shorter, more efficient solution. Any suggestions?

Answer 1

One basic way is using a NOT EXISTS:

SELECT TableID FROM Table t1
where NOT EXISTS (select * from BlackList b where b.TableID = t1.TableID);

This will select rows in t1 that are not present in the BlackList table.