SQL Find list of tuples that fulfil at least one of the conditions

Question: Find the restaurant A that fulfils at least one of the following conditions:

Conditions

1. Restaurant A that is situated in ‘Central’ area or
2. Restaurant A that sells at least 10 pizzas or
3. Price of every pizza sold by A is at most $20

Expected outcomes: List with (restaurant name)

Database Schema: Customers(cname, area), Restaurants(rname, area), Pizzas(pizza), Sells(rname,pizza,price), Likes(cname, pizza)

Restaurants Table

  rname  |  area   
---------+---------
 Alpha   | East
 Beta    | East
 Gamma   | Central
 Delta   | Central
 Epsilon | North
 Zeta    | North
 Eta     | South
 Theta   | South
 Iota    | West
 Lambda  | West

Sells table

  rname  |   pizza    | price 
---------+------------+-------
 Gamma   | Funghi     |    30
 Gamma   | Margherita |    30
 Gamma   | Marinara   |    19
 Delta   | Funghi     |    34
 Delta   | Margherita |    15
 Delta   | Marinara   |    22
 Epsilon | Hawaiian   |    28
 Zeta    | Funghi     |    17
 Eta     | Marinara   |    24
 Theta   | Diavola    |    15
 Theta   | Hawaiian   |    26
 Iota    | Funghi     |    27
 Lambda  | Diavola    |    21
 Lambda  | Funghi     |    30
 Lambda  | Hawaiian   |    16
 Lambda  | Margherita |    18
 Lambda  | Marinara   |    32

My SQL Query

SELECT DISTINCT R.rname
FROM Restaurants R
NATURAL JOIN Sells S
WHERE (
    (CASE WHEN (R.area = 'Central') THEN 1 ELSE 0 END) +
    (CASE WHEN ((SELECT COUNT(DISTINCT S2.pizza) FROM Sells S2 WHERE R.rname = S2.rname)>= 10) THEN 1 ELSE 0 END) +
    (CASE WHEN (S.price <= 20) THEN 1 ELSE 0 END) 
) >= 1;

Issue I cant seem to get the correct answer for what the question is asking for. Appreciate if you can help me to see what is wrong with my sql query.

Answer

I think I would use subqueries in the where clause for this:

select r.*
from restaurants r
where r.location = 'Central' or
      (select count(*)
       from sells s
       where s.rname = r.rname
      ) >= 10 or
      (select max(s.price)
       from sells s
       where s.rname = r.rname
      ) <= 20;

There are ways to handle this query using JOIN and aggregation as well:

select r.*
from restaurants r left join
     sells s
     using (rname)
group by r.rname  -- assumes this is a unique or primary key
having r.location = 'Central' or
       count(*) >= 10 or
       max(s.price) <= 20;

Both of these assume that the sells table has only pizzas.