I have this problem to solve: **If two students A and B are friends, and A likes B but not vice-versa, remove the Likes entry**. 

For background, the Friend table has two columns, STU1 and STU2. If they are friends, then there will be an entry showing STU1, STU2 AND STU2, STU1. 

In the Likes table, if Student A likes Student B, there will be an entry for STU1, STU2, but if Student B does not like Student A, there will NOT be an entry for STU2, STU1.

So, here is what I have tried. The problem is that it still leaves two rows in the Likes table that should be out of there. Any ideas on how to solve this on?

```
delete from Likes
where exists 
    (select F.STU1, F.STU2 from Friend F
        where exists  
        (select L.STU1, L.STU2 from Likes L, Friend F where
            F.STU1 = L.STU1 and F.STU2 = L.STU2)
        )
    and not exists
        (select L.STU1, L.STU2 from Likes L, Friend F where
            F.STU1 = L.STU2 and F.STU2 = L.STU1)

```