SQL: exact row match given certain elements - mysql

Question

this is my first time posting here. I don't seem to find the answer to my problem.
So... I'm arranging a DB for a school project, a cookbook that only shows recipes that can be made with existing elements from the "shelf".
These ingredients have to have an exact ingredients match.
user:
+---------------+------+----------+----------+
| email | name | lastname | password |
+---------------+------+----------+----------+
| pal#mail.com | John | Potato | password |
| they#mail.com | Mary | Carrot | password |
+---------------+------+----------+----------+
shelf:
+---------+------------+---------------+
| shelfID | ingredient | user |
+---------+------------+---------------+
| 1 | 1 | pal#mail.com |
| 2 | 2 | pal#mail.com |
| 3 | 3 | pal#mail.com |
| 4 | 4 | pal#mail.com |
| 5 | 10 | they#mail.com |
| 6 | 12 | they#mail.com |
+---------+------------+---------------+
This is my recipe_ingredient relationship table
recipe_ingredient:
+--------+------------+
| recipe | ingredient |
+--------+------------+
| 1 | 1 |
| 1 | 2 |
| 1 | 4 |
| 1 | 10 |
| 2 | 1 |
| 2 | 2 |
| 2 | 3 |
| 2 | 4 |
| 3 | 2 |
| 3 | 3 |
| 3 | 15 |
+--------+------------+
I've tried this query:
SELECT
rec_ing.recipe, shf.ingredient, shf.user
FROM
recipes_ingredients AS rec_ing
INNER JOIN
shelf AS shf ON rec_ing.ingredient = shf.ingredient
INNER JOIN
users AS usr ON shf.user = usr.email
WHERE
usr.email = 'pal#mail.com'
that returns this table:
+--------+------------+--------------+
| recipe | ingredient | user |
+--------+------------+--------------+
| 1 | 1 | pal#mail.com |
| 1 | 2 | pal#mail.com |
| 1 | 4 | pal#mail.com |
| 2 | 1 | pal#mail.com |
| 2 | 2 | pal#mail.com |
| 2 | 3 | pal#mail.com |
| 2 | 4 | pal#mail.com |
| 3 | 2 | pal#mail.com |
| 3 | 3 | pal#mail.com |
+--------+------------+--------------+
Although it's true that the Recipe 1 contains ingredients from my shelf, it's also missing Ingredient 10
+--------+------------+
| recipe | ingredient |
+--------+------------+
| 1 | 1 |
| 1 | 2 |
| 1 | 4 |
| 1 | 10 |
| ... | ... |
+--------+------------+
I'm trying to only get this kind of result set.
+--------+------------+
| recipe | ingredient |
+--------+------------+
| 2 | 1 |
| 2 | 2 |
| 2 | 3 |
| 2 | 4 |
+--------+------------+
Because Recipe 2 contains all elements from my shelf
I have been going around all day with this problem ... What could be missing?

Answer 1

This is a bit tricky, because you need to aggregate your current query by recipe, but you also need the original query to get back the full records. Sadly, MySQL does not support common table exprrssions or other features which could give us a less verbose query.
SELECT
rec_ing.recipe,
shf.ingredient,
shf.user
FROM recipes_ingredients AS rec_ing
INNER JOIN shelf AS shf
ON rec_ing.ingredient = shf.ingredient
INNER JOIN users AS usr
ON shf.user = usr.email
INNER JOIN
(
SELECT rec_ing.recipe
FROM recipes_ingredients AS rec_ing
INNER JOIN shelf AS shf
ON rec_ing.ingredient = shf.ingredient
LEFT JOIN users AS usr
ON shf.user = usr.email
WHERE
usr.email = 'pal#mail.com'
GROUP BY rec_ing.recipe
HAVING COUNT(usr.email) = COUNT(*)
) t
ON rec_ing.recipe = t.recipe
WHERE
usr.email = 'pal#mail.com'
The basic strategy here is to just do one additional join to a subquery which identifies all recipes where every ingredient belongs to a given user. The critical part is the following:
HAVING COUNT(usr.email) = COUNT(*)
This checks that the total number of rows for a given recipe matches the number of rows which have been assigned to a given user.