How to join a parent table to two child tables without duplication?

Question

parent table:

id	city_name	zip_code
1	new york city	10001
2	los angeles	90001
3	chicago	60007

Customer, child table:

id	customer_name	city_id	address
1	alice	1	428 Hartford Lane
2	betty	1	249 George Street
3	cath	3	12112 S Front Ave
4	daph	3	8619 S Wolcott Ave

Restaurant, child table:

id	address	city_id
1	256 Roehampton St.	1
2	920 Cherry Camp Road	3
3	7609 Mckinley Ave	2
4	5723 Morgan Ave	2

When using the following query:

select c.id, c.city_name, c.zip_code, r.id, r.address, r.city_id, cus.id, cus.customer_name, cus.city_id, cus.address 
from restaurant r 
left join city c 
    on r.city_id = c.id 
right join customer cus 
    on c.id = cus.city_id where c.id = 1;

There will be a duplicate restaurant address entry. How do I ensure that the restaurants and customers are distinct?

id	city_name	zip_code	id	address	city_id	id	customer_name	city_id	address
1	new york city	10001	1	256 Roehampton St.	1	1	alice	1	428 Hartford Lane
1	new york city	10001	1	256 Roehampton St.	1	2	betty	1	249 George Street

***Edit: To add some context, I would like to return a json object of a city which contains its fields as well as a list of customers and a list of restaurants belonging to that particular city.

Is it more efficient to make three separate queries to populate that object, i.e.

select * from city where id = 1;
select * from customer where city_id = 1;
select * from restaurant where city_id = 1;

or perform one query with two joins, with the expected result as the following, where there are no duplicate restaurants or customers

id	city_name	zip_code	id	address	city_id	id	customer_name	city_id	address
1	new york city	10001	1	256 Roehampton St.	1	1	alice	1	428 Hartford Lane
1	new york city	10001				2	betty	1	249 George Street

Or can I just use a distinct keyword to remove duplicates?

Answer 1

What you're looking to do is denormalize your data into a JSON object. This is usually not a standard thing to do from a relational database, but PostgreSQL has a cool function that makes it possible called row_to_json(). You should be able to distinctify your JSON object using that function accordingly on top of your query's result set.

Answer 2

Short answer - use two queries.

Restaurants appear in a city.
Customers appear in a city.
I see no relationship between Restaurants and Customers, so there's no way to "remove the duplication" that you're seeing.

You have two different sets of data, here, so use two different queries to retrieve them.