How to optimize m:n relation query on 3 tables - sql

Question

this is my sql problem - there are 3 tables:
Names Lists ListHasNames
Id Name Id Desc ListsId NamesId
=-------- ------------ ----------------
1 Paul 1 Football 1 1
2 Joe 2 Basketball 1 2
3 Jenny 3 Ping Pong 2 1
4 Tina 4 Breakfast Club 2 3
5 Midnight Club 3 2
3 3
4 1
4 2
4 3
5 1
5 2
5 3
5 4
Which means that Paul (Id=1) and Joe (Id=2) are in the Football team (Lists.Id=1), Paul and Jenny in the Basketball team, etc...
Now I need a SQL statement which returns the Lists.Id of a specific Name combination:
In which lists are Paul, Joe and Jenny the only members of that list ? Answer only Lists.Id=4 (Breakfast Club) - but not 5 (Midnight Club) because Tina is in that list, too.
I've tried it with INNER JOINS and SUB QUERIES:
SELECT Q1.Lists_id FROM
(
SELECT Lists_Id FROM
names as T1,
listhasnames as T2
WHERE
(T1.Name='Paul') and
(T1.Id=T2.Names_ID) and
( (
SELECT count(*) FROM
listhasnames as Z1
where (Z1.lists_id = T2.lists_Id)
) = 3)
) AS Q1
INNER JOIN (
SELECT Lists_Id FROM
names as T1,
listhasnames as T2
WHERE
(T1.Name='Joe') and
(T1.Id=T2.Names_ID) and
(
(SELECT count(*) FROM
listhasnames as Z1
WHERE (Z1.Lists_id = T2.lists_id)
) = 3)
) AS Q2
ON (Q1.Lists_id=Q2.Lists_id)
INNER JOIN (
SELECT Lists_Id FROM
names as T1,
listhasnames as T2
WHERE
(T1.Name='Jenny') and
(T1.Id=T2.Names_ID) and
(
(SELECT count(*) FROM
listhasnames as Z1
WHERE (Z1.Lists_id = T2.lists_id)
) = 3)
) AS Q3
ON (Q1.Lists_id=Q3.Lists_id)
Looks a little bit complicated, uh? How to optimize that?
I need only that Lists.Id in which specific names are in (and only these names and nobody else). Maybe with SELECT IN?
Regards,
Dennis

Answer 1

SELECT ListsId
FROM ListHasNames a
WHERE NamesId in (1, 2, 3)
AND NOT EXISTS
(SELECT * from ListHasNames b
WHERE b.ListsId = a.ListsId
AND b.NamesId not in (1, 2, 3))
GROUP BY ListsId
HAVING COUNT(*) = 3;
Edit: Corrected thanks to Chris Gow's comment; the subselect is necessary to exclude lists that have other people on them.
Edit 2 Corrected the table name thanks to Dennis' comment

Answer 2

Using Carl Manaster's solution as a starting point I came up with:
SELECT listsid
FROM listhasnames
GROUP BY listsid HAVING COUNT(*) = 3
INTERSECT
SELECT x.listsid
FROM listhasnames x, names n
WHERE n.name IN('Paul', 'Joe', 'Jenny')
AND n.id = x.namesid

Answer 3

Updated:
select a.ListsId from
(
--lists with three names only
select lhn.ListsId, count(*) as count
from ListHasNames lhn
inner join Names n on lhn.NamesId = n.Id
group by lhn.ListsId
having count(*) = 3
) a
where a.ListsId in (select ListsId from ListHasNames lhn where NamesId = (select NamesId from names where Name = 'Paul'))
and a.ListsId in (select ListsId from ListHasNames lhn where NamesId = (select NamesId from names where Name = 'Joe'))
and a.ListsId in (select ListsId from ListHasNames lhn where NamesId = (select NamesId from names where Name = 'Jenny'))

Answer 4

I was just solving a problem recently that may work well for your case as well. It may be overkill.
I took the approach of creating a list of candidate associations that may be the correct solution, and then using a cursor or queue table to go through the likely correct solutions to do full validation.
In my case this was implemented by doing like
select
ParentId
count(*) as ChildCount
checksum_agg(checksum(child.*) as ChildAggCrc
from parent join child on parent.parentId = child.parentId
Then you can compare the count and aggregate checksum against your lookup data (i.e. your 3 names to check for). If no rows match, you are guaranteed to have no matches. If any row matches you can then go through and do a join of that specific ParentId to validate if there are any discrepancies between the row sets.
Clear as mud? :)