Question

Schema

I have 3 tables with the following columns:

tblClients [ClientID, ClientName, Client Contact]
tblEvents [EventID, EventName]
tblEventBook [EventBookID, EventID, ClientID]

• tblEventBook EventID matches tblEvents EventID
• tblEventBook ClientID matches tblClients ClientID

I have two parameters: @useEventID and @useClientID

I would like to retrieve all rows from tblClient where tblEventBook does not equal useEventID and useClientID.

I tried to use the below, but it does not work:

SELECT * 
FROM tblClients 
WHERE tblEventBook.EventID <> @useEventID 
  AND tblEventBook.ClientID <> @useClientID

Sample Data:

tblEventBook

EventBookID EventID ClientID 
1           1          1 
2           2          2
3           3          1
4           4          2

tblClients

ClientID ClientName  ClientContact
1        TestNameA   12345
2        TestNameB   54321

tblEvents

EventID EventName
1       TestEventA
2       TestEventB
3       TestEventC
4       TestEventD
5       TestEventE

Required results

I need to get the below results when I use:

1. @useClientID = 1, @useEventID = 1

   It should return ClientID 2

2. @useClientID = 2, @useEventID = 1

   It should return ClientID 1 and 2

3. @useClientID = 2, @useEventID = 2

   It should return ClientID 1

4. @useClientID = 5, @useEventID = 2

   It should return ClientID 1 and 2

Answer 1

This solution will exclude all tblClients with @useClientID and related tblEventBook that match @useEventID:

select * from tblClients c
where c.ClientID <> @useClientID
and not exists(select 1 from tblEventBook where ClientID=c.ClientID and EventID=@useEventID)

But from your description I also see a slightly difference possibility, where we only exclude tblClients if a related tblEventBook record exists having @useClientID and @useEventID:

select * from tblClients c
where not exists(
    select 1 from tblEventBook 
    where ClientID=c.ClientID 
    and EventID=@useEventID
    and ClientID=@useClientID
)