sql finding multiple characters within multiple books - sql

Question

I can't seem to find all comics with certain characters in them. The comics and characters tables have a many to many relationship as follows:
My database schema:
**comics table**
comic_id
comic_name
comic_date
**character table**
character_id
character_name
**comics_character table**
comic_id
character_id
This works fine for one character:
sqlite3 comics.db
select comic_name
from comics as c, comics_characters as cc, characters as h
on c.comic_id = cc.comic_id and h.character_id = cc.character_id
where h.character_name = 'Superman';
But if I want all comics with say Superman and Batman in them, I tried using this:
sqlite3 comics.db
select comic_name
from comics as c, comics_characters as cc, characters as h
on c.comic_id = cc.comic_id and h.character_id = cc.character_id
where h.character_name in ('Batman', 'Superman');
but this only gets me a list of comics featuring either Batman OR Superman rather than comics with both Batman AND Superman in
I've also tried this which doesn't return anything:
sqlite3 comics.db
select comic_name
from comics as c, comics_characters as cc, characters as h
on (c.comic_id = cc.comic_id and h.character_id = cc.character_id)
where (h.character_name = 'Batman' and h.character_name = 'Superman');
I've tried other variations but can't get the desired result

Answer 1

The OR route doesn't work, for reasons you've worked out - you get rows for superman or batman, and comics that have both characters have two rows with the same comic is and different character ids. The AND route doesn't work because a row cannot be simultaneously both characters.
So, you need to use the OR route to get comics with one or both characters and then also use a count to show only comics with both characters. Essentially, "filter to superman or batman, and then filter again to only comic ids that appear on two rows" or "filter to only batman or superman then group them up based on the comic is and only take Groups that have two entities in them". Ultimately, the lesson here is that database rows are thought of as different entities and when you want to treat them as one you have to group them, so we are identifying comics based on some attribute of the group after (deliberately) losing the detail of exactly which entities the group contains:
SELECT comic_id
FROM comic_characters
WHERE character_id IN (1,2) --Batman or Superman
GROUP BY conic_id
HAVING COUNT(*) = 2
The number on the right hand side of the = must be the same as the number of character IDs in the IN() clause. If you IN for 4 character IDs, then use COUNT(*) = 4
You can join in other tables so you can use names etc; I simplified this to make the point without extraneous detail
Footnote; this technique wil find comics that feature at least batman and superman- the comic could very well contain other characters too but we lost those other guys at the WHERE stage before we did the GROUP BY. If you wanted comics that ONLY featured batman and superman it's a different thing. For that we could do something like grouping first, and counting conditionally - give batman or superman a score of 1 and everyone else a score of 10, comics that had only B and S would score 2, comics that featured only one of them would score 1 and anyone else's presence would cause a score of 10 or more, so we could filter on the 2