Question

recipe_category

cid | category
 1  | desserts
 2  | cakes
 3  | biscuits

recipe_name

id | recipe_name       | cid | iid
 1 | black forest cake | 1,2 | 1,2,3,4
 2 | angel cake        | 2   | 1,2,4
 3 | melting moments   | 3   | 2,5
 4 | croquembouche     | 1,3 | 1,5

ingredients

iid | ingredient_name
 1  | self-raising flour
 2  | milk
 3  | chocolate
 4  | baking powder
 5  | plain flour

I am able to query the DB using cid to pull certain recipes, ie. desserts:

SELECT * FROM recipe_name WHERE cid='1'

But then how do I create a list of ingredients like the below where ingredients are listed with <br>?

Black Forest Cake:
Self-Raising Flour
Milk
Chocolate
Baking Powder

I’m new to this, so please forgive any stupid questions!

Answer 1

Storing multivalued attributes in a single comma separated field is almost always a bad idea. It makes everything very difficult to query.

Instead, you may want to consider refactoring your schema, using two new intersection tables.

These two tables remain as they are (just changed name of recipe_category to categories in order not to clash with the intersection table):

CREATE TABLE categories (
   cid int NOT NULL PRIMARY KEY,
   category_name varchar(50)
) ENGINE=INNODB;

CREATE TABLE ingredients (
   iid int NOT NULL PRIMARY KEY,
   ingredient_name varchar(50)
) ENGINE=INNODB;

Modify the recipe_name table as follows, removing the cid and iid fields:

CREATE TABLE recipe_name (
    id int NOT NULL PRIMARY KEY,
    recipe_name varchar(50)
) ENGINE=INNODB;

Then you can define your multivalued relationships using the following two intersection tables:

CREATE TABLE recipe_ingredients (
    recipe_id int NOT NULL,
    ingredient_id int NOT NULL,
    PRIMARY KEY (recipe_id, ingredient_id),
    FOREIGN KEY (recipe_id) REFERENCES recipe_name (id),
    FOREIGN KEY (ingredient_id) REFERENCES ingredients (iid)
) ENGINE=INNODB;

CREATE TABLE recipe_categories (
    recipe_id int NOT NULL,
    category_id int NOT NULL,
    PRIMARY KEY (recipe_id, category_id),
    FOREIGN KEY (recipe_id) REFERENCES recipe_name (id),
    FOREIGN KEY (category_id) REFERENCES categories (cid)
) ENGINE=INNODB;

Now let’s populate these tables with your example data:

INSERT INTO categories VALUES (1, 'desserts');
INSERT INTO categories VALUES (2, 'cakes');
INSERT INTO categories VALUES (3, 'biscuits');

INSERT INTO ingredients VALUES(1, 'self-raising flour');
INSERT INTO ingredients VALUES(2, 'milk');
INSERT INTO ingredients VALUES(3, 'chocolate');
INSERT INTO ingredients VALUES(4, 'baking powder');
INSERT INTO ingredients VALUES(5, 'plain flour');

INSERT INTO recipe_name VALUES(1, 'black forest cake');
INSERT INTO recipe_name VALUES(2, 'angel cake');
INSERT INTO recipe_name VALUES(3, 'melting moments');
INSERT INTO recipe_name VALUES(4, 'croquembouche'); 

To define the relationships between the recipes and their ingredients and categories, you would need to fill up the intersection tables as follows:

INSERT INTO recipe_categories VALUES (1, 1);
INSERT INTO recipe_categories VALUES (1, 2);
INSERT INTO recipe_categories VALUES (2, 2);
INSERT INTO recipe_categories VALUES (3, 3);
INSERT INTO recipe_categories VALUES (4, 1);
INSERT INTO recipe_categories VALUES (4, 3);

INSERT INTO recipe_ingredients VALUES (1, 1);
INSERT INTO recipe_ingredients VALUES (1, 2);
INSERT INTO recipe_ingredients VALUES (1, 3);
INSERT INTO recipe_ingredients VALUES (1, 4);
INSERT INTO recipe_ingredients VALUES (2, 1);
INSERT INTO recipe_ingredients VALUES (2, 2);
INSERT INTO recipe_ingredients VALUES (2, 3);
INSERT INTO recipe_ingredients VALUES (3, 2);
INSERT INTO recipe_ingredients VALUES (3, 5);
INSERT INTO recipe_ingredients VALUES (4, 1);
INSERT INTO recipe_ingredients VALUES (4, 5);

Finally, building your query will be as easy as this:

SELECT i.ingredient_name
FROM   recipe_ingredients ri
JOIN   ingredients i ON (i.iid = ri.ingredient_id)
WHERE  ri.recipe_id = (SELECT id 
                       FROM   recipe_name 
                       WHERE  recipe_name = 'Black Forest Cake');

Result:

+--------------------+
| ingredient_name    |
+--------------------+
| self-raising flour |
| milk               |
| chocolate          |
| baking powder      |
+--------------------+
4 rows in set (0.00 sec)

You may then want to format that result set (adding the <br>s) in your application code instead of in SQL.

However if you really wish to do that in SQL, then MySQL supports the handy GROUP_CONCAT() function, which can be used as follows:

SELECT GROUP_CONCAT(i.ingredient_name separator '<BR>') output
FROM   recipe_ingredients ri
JOIN   ingredients i ON (i.iid = ri.ingredient_id)
WHERE  ri.recipe_id = (SELECT id 
                       FROM   recipe_name 
                       WHERE  recipe_name = 'Black Forest Cake');

Result:

+----------------------------------------------------------+
| output                                                   |
+----------------------------------------------------------+
| self-raising flour<BR>milk<BR>chocolate<BR>baking powder |
+----------------------------------------------------------+
1 row in set (0.00 sec)

Dump that into HTML, and you’re good to go!