Question

Ok, sorry if this is a repost, I really don’t know how to word what I’m looking for to really search for it.

I have 3 tables:

Amenities:
AmenitiesID
Name

resort_amenities
ResortAmenitiesID
ResortID
AmenityID

resorts
ResortID
ResortName
and so on...

I am working on the code that links the amenties to the resort, and saved in resort_amenities.

What I want is to have a jQuery modal dialog come up with all the amenities from the amenities table, that aren’t already linked to that resort.

Right now in my ajax call I pass the resort id, to be used in the sql somewhere.

I believe I need a union but have never built one, out side of school years ago.

Thanks

Answer 1

So you want, for a specific resort, the set of amenities not associated with that resort:

SELECT DISTINCT * -- get all those Amenities
FROM Amenities
WHERE NOT EXISTS ( -- that we can't find a counter-example for
  SELECT AmenitiesID 
  From resort_amenities 
  WHERE ResortID = <the resort id>
  AND Amenities.AmenitiesID = resort_amenities.AmenitiesID
)

This is a set substraction, of S = S1 - S2, where S1 is the set of all amenities, and S2 is the set of amenities that are already linked to that resort.