Question

I don’t know if my title correctly conveys the query I’m trying to achieve, so please edit or suggest a better one that is more correct. I’m trying to join these two tables together:

Table 1: people

id |field1|field2|
------------------
1  
2
3
4
.
.
. (etc)

Table 2: foods

person.id | name
1         | chicken
1         | pork
1         | beef
2         | pork
2         | chicken
3         | chicken
4         | beef
.
. (etc)

I need to join these tables based on a search for any people whose ID is matched with both pork or chicken. For example, if I search for pork, 1 and 2 should be returned, and if I search for pork and chicken, 1 and 2 should still be returned, but 3 will not be because it doesn’t match chicken as well as pork. If I search for pork, chicken, and beef, only 1 should be returned.

I’ve been looking at this question, but I don’t know how many items I’ll be searching for (I could be searching for pork and chicken one time, and pork, chicken, or beef another time).

I started out trying the basic WHERE clause, which I was fairly certain was faulty (I confirmed this because the query didn’t work):

SELECT p.id 
FROM people p, foods f 
WHERE p.id = f.person_id AND (f.name = 'pork' AND f.name = 'chicken')

but this returns no results. I seem to remember from an SQL tutorial several years ago that I should be using the EXISTS keyword along with a subquery, but I’m not sure how to shape my query/queries based on that.

EDIT: SQL Server CE doesn’t support the INTERSECT keyword, so unfortunately that option isn’t available to me.

Answer 1

If you can costruct your list ('chicken', 'pork', 'beef') and count the items in your application:

SELECT p.*
FROM   people AS p
  JOIN (
   SELECT person_id
   FROM   foods
   WHERE  name IN ('chicken', 'pork', 'beef')   --- list
   GROUP  BY person_id
   HAVING COUNT(*) = 3                          --- list size
   ) AS pf ON pf.person_id = p.id ;