SELECT common entities only based on different corresponding entities - sql

Question

3 Tables
Client -
CID Name
1 Ana
2 Bana
3 Cana
ClientProgram (Bridge Table) -
CID PID
1 4
1 5
1 8
2 10
Program -
PID Program
4 X
5 Y
8 Z
10 G
Desired Output:
Name Program
Ana X
Ana Y
I want to extract only those Clients which are common/exist in different Programs I choose (say X and Y in this case)
Query attempt:
SELECT
C.Name
,P.Program
FROM ClientProgram CP
INNER JOIN Client C
ON CP.CID=C.CID
INNER JOIN Program P
ON CP.PID=P.PID
INNER JOIN ClientProgram CP1
ON CP.CID=CP1.CID
WHERE P.Program = 'X' OR P.Program = 'Y'
AND CP.CID = CP1.CID
This however doesn't pulls in all clients and not only those which exist in multiple programs.

Answer 1

;WITH cte AS (
SELECT
c.Name
,p.Program
,COUNT(*) OVER (PARTITION BY c.CID) as ProgramCount
FROM
Program p
INNER JOIN ClientProgram cp
ON p.PID = cp.PID
INNER JOIN Client c
On cp.CID = c.CID
WHERE
p.Program IN ('X','Y')
)
SELECT Name, Program
FROM
cte
WHERE
ProgramCount > 1
The use of COUNT(*) over will be a problem if PID is not unique in Programs or if the combination of CID to PID in ClientProgram is not unique. However I would assume uniqueness based on what I see.
If not you can go a route like this:
;WITH cte AS (
SELECT
cp.CID
FROM
Program p
INNER JOIN ClientProgram cp
ON p.PID = cp.PID
WHERE
p.Program IN ('X','Y')
GROUP BY
cp.CID
HAVING
COUNT(DISTINCT p.PID) > 1
)
SELECT
c.Name
,p.Program
FROM
cte t
INNER JOIN Client c
ON t.CID = c.CID
INNER JOIN ClientProgram cp
ON t.CID = cp.CID
INNER JOIN Program p
ON cp.PID = p.PID
AND p.Program IN ('X','Y')

Answer 2

This is kind of a round about way of doing it. Probably a better way but this will do it. I through in scripts for temp table in case someone else wants to improve. Could do a temp table for example instead of CTE.
create table #client(cid int,name varchar(20))
create table #clientprogram (cid int, pid int)
create table #program( pid int, program varchar(20))
insert into #client
values(1,'Ana')
,(2,'Bana')
,(3,'Cana')
insert into #clientprogram
values (1,4)
,(1,5)
,(1,8)
,(2,10)
,(2,4)
insert into #program
values (4,'x')
,(5,'y')
,(8,'z')
,(10,'g')
WITH CHECKPLEASE AS(
Select c.Name,ISNULL(p.Program,p2.PRogram) Program
from #client c
inner join #clientprogram cp
on c.CID = cp.CID
left join #program p
on cp.PID = p.PID
and p.PRogram = 'X'
left join #program p2
on cp.PID = p2.PID
and p2.Program = 'Y'
where ISNULL(p.Program,p2.PRogram) is not null
)
Select *
From CHECKPLEASE
where Name in (
SELECT Name
From CHECKPLEASE
group by Name
having COUNT(*) > 1)