Join operations in SQL - sql

Question

I should retrieve the IDs and names of ingredients that are not contained by any ice cream and then
sort the output rows in ascending order by ingredient ID. I don't quite understand how JOIN -operation works in this exercise.
I tried e.g. the following but it gives too many rows in the output.
SELECT ingredient.ingredient_id, ingredient.ingredient_name
FROM ingredient
LEFT JOIN contains ON ingredient.ingredient_id != contains.ingredient_id
LEFT JOIN ice_cream ON ice_cream.ice_cream_id != contains.ice_cream_id
ORDER BY ingredient.ingredient_id;
Output columns should be as follows:
ingredient_id ingredient_name
----------------------------
6 Dark chocolate
and here are the tables:
CREATE TABLE manufacturer (
manufacturer_id INT,
manufacturer_name VARCHAR(30) NOT NULL,
country VARCHAR(30) NOT NULL,
PRIMARY KEY (manufacturer_id),
UNIQUE (manufacturer_name)
);
-- jäätelöitä
-- ice creams
CREATE TABLE ice_cream (
ice_cream_id INT,
ice_cream_name VARCHAR(30) NOT NULL,
manufacturer_id INT NOT NULL,
manufacturing_cost NUMERIC(4,2),
PRIMARY KEY (ice_cream_id),
UNIQUE (ice_cream_name),
FOREIGN KEY (manufacturer_id) REFERENCES manufacturer
);
-- aineksia
-- ingredients
-- plant_based arvo 0 merkitse ei ja arvo 1 merkitsee kyllä
-- plant_based value 0 means no and value 1 means yes
CREATE TABLE ingredient (
ingredient_id INT,
ingredient_name VARCHAR(30) NOT NULL,
kcal INT,
protein NUMERIC(3,1),
plant_based INT,
PRIMARY KEY (ingredient_id),
UNIQUE (ingredient_name)
);
-- jäätelöt sisältävät aineksia
-- ice creams contain ingredients
CREATE TABLE contains(
ice_cream_id INT NOT NULL,
ingredient_id INT NOT NULL,
quantity INT,
PRIMARY KEY (ice_cream_id, ingredient_id),
FOREIGN KEY (ice_cream_id) REFERENCES ice_cream,
FOREIGN KEY (ingredient_id) REFERENCES ingredient
);
--Ice cream manufacturers
INSERT INTO manufacturer VALUES (
1, 'Jen & Berry', 'Canada'
);
INSERT INTO manufacturer VALUES (
2, '4 Friends', 'Finland'
);
INSERT INTO manufacturer VALUES (
3, 'Gelatron', 'Italy'
);
--Ice cream
INSERT INTO ice_cream VALUES (
1, 'Plain Vanilla', 1, 1.00
);
INSERT INTO ice_cream VALUES (
2, 'Vegan Vanilla', 2, 0.89
);
INSERT INTO ice_cream VALUES (
3, 'Super Strawberry', 2, 1.44
);
INSERT INTO ice_cream VALUES (
4, 'Very plain', 2, 1.20
);
--Ingredients
INSERT INTO ingredient VALUES (
1, 'Cream', 400, 3, 0
);
INSERT INTO ingredient VALUES (
2, 'Coconut cream', 230, 2.3, 1
);
INSERT INTO ingredient VALUES (
3, 'Sugar', 387, 0, 1
);
INSERT INTO ingredient VALUES (
4, 'Vanilla extract', 12, 0, 1
);
INSERT INTO ingredient VALUES (
5, 'Strawberry', 33, 0.7, 1
);
INSERT INTO ingredient VALUES (
6, 'Dark chocolate', 535, 8, 1
);
--Contains
INSERT INTO contains VALUES (
1, 1, 70
);
INSERT INTO contains VALUES (
1, 3, 27
);
INSERT INTO contains VALUES (
1, 4, 3
);
INSERT INTO contains VALUES (
2, 2, 74
);
INSERT INTO contains VALUES (
2, 3, 21
);
INSERT INTO contains VALUES (
2, 4, 5
);
INSERT INTO contains VALUES (
3, 1, 60
);
INSERT INTO contains VALUES (
3, 3, 10
);
INSERT INTO contains VALUES (
3, 5, 30
);
INSERT INTO contains VALUES (
4, 2, 95
);
INSERT INTO contains VALUES (
4, 4, 5
);

Answer 1

You can join the "contains" table with the "ingredient" table using a LEFT JOIN and filter all values that have NULL in the "contains.ice_cream_id" field:
SELECT i.ingredient_id,
i.ingredient_name
FROM ingredient i
LEFT JOIN contains c
ON i.ingredient_id = c.ingredient_id
WHERE c.ice_cream_id IS NULL

Answer 2

It appears you are asking to find where somethig does not exist, so it would make sense to express that using not exists
So you just need to find the ingredients that don't exist in the list of contents:
select ingredient_id, ingredient_name
from ingredient i
where not exists (
select * from contains c
where c.ingredient_id = i.ingredient_id
);
Demo Fiddle