SQL Database Model: FOOD and INGREDIENTS tables - sql

Question

I have 2 tables: FOOD and INGREDIENTS. I want to select all ingredients that are necessary to make certain food.
I thought I could do something like this:
select NAME from INGREDIENTS
where ID in (select ING1_ID, ING2_ID, ING3_ID from FOOD where NAME = 'Meat soup')
That obviously doesn't work as I need to pass a string of comma separated IDs in the "in" sub-select query. I was looking into converting list of column values into a string and there are some solutions out there but I started to think that maybe I'm over-complicating this and my database model is wrong.
FOOD Table:
ID | NAME | ING1_ID | ING2_ID | ING3_ID
--------+---------------+----------+----------+--------
1 | Meat soup | 1 | 2 | 3
2 | Pasta Bolo | 3 | 4 | 5
3 | Chicken salad | 2 | 4 | 5
INGREDIENTS Table:
ID | NAME
--------+-----------
1 | pasta
2 | onion
3 | oil
4 | paprika
5 | chicken
6 | cucumber

Answer 1

Many dishes have more than three ingredients, and when you're searching, you don't care about whether a given ingredient is #1 or #2 or #3.
So a better model is
FOOD
id | name
1 | meat soup
INGREDIENTS
id | name
1 | meat
FOOD_INGREDIENTS
food_id | ingredients_id
1 | 1
Now your query is just
select i.name from ingredients i, food f, food_ingredients fi
where fi.food_id = f.id
and fi.ingredients_id = i.id
and f.name = "meat soup"
The "food_ingredients" table is often called a "join table". Another nice thing about a join table is that you can add information that's specific to the particular inclusion of an ingredient in a kind of food (such as amount, or how it should be prepared).

Answer 2

Your problems stem from the fact that you do not have a normalized data model.
You should redesign into something like this:
FOOD table:
FoodID
Name
INGREDIENTS table:
IngID
Name
FOOD2INGREDIENTS table:
FoodID
IngID
(adding quantity here would make a lot of sense)
Once such a redesign had been made you could get what you want simply by querying:
SELECT i.ID, I.Name
FROM Ingredients I
INNER JOIN Food2Ingredients F2I
ON I.IngID = F2I.IngID
WHERE
F2I.FoodID = :foodid;

Answer 3

As long as all your recipes are so impoverished as to require exactly three ingredients, then you can resolve the problem with the original query by writing:
SELECT Name FROM Ingredients
WHERE ID IN (SELECT ING1_ID FROM Food WHERE Name = 'Meat soup'
UNION
SELECT ING2_ID FROM Food WHERE Name = 'Meat soup'
UNION
SELECT ING3_ID FROM Food WHERE Name = 'Meat soup'
)
However, I think JacobM and Kerbocat are onto the right idea with the database redesign, and your sense that there was something wrong with your database design is to be commended. Note that if you need a recipe with 4 (or more) ingredients, you face a disaster with the current design (for example, because you have to edit all the existing SQL which includes multi-way UNION operations like the one shown above), but the redesigned schemas wouldn't even notice.