How to show the results as zero when there is no record

I have the 3 tables below with the following data

create table model (
id int comment 'The model id. Primary Key',
name varchar(50) comment 'Models name',
price int comment 'The price of the model',
primary key (id)
);

create table country (
id int comment 'The country id. Primary Key',
name varchar(50) comment 'Countrys name',
primary key (id)
);

create table sales (
model_id int comment 'Models id',
country_id int comment 'Countrys id',
quantity int comment 'Number of units sold',
sales_date date comment 'Date of the sale'
);

INSERT INTO COUNTRY VALUES
(1, 'Brazil'),
(2, 'Italy'),
(3, 'China');

INSERT INTO model VALUES
(1, 'ZTX100', 100),
(2, 'AHT567', 200),
(3, 'JPF090', 300);

INSERT INTO sales VALUES
(1, '1', 500, '2017-01-10'),
(2, '2', 600, '2017-05-11'),
(3, '3', 700, '2017-07-21'),
(1, '3', 200, '2019-08-14');

I need to write a query that calculates country-wise sales for all of the models along with the revenue generated for the year 2017. The result should be in the following format: country_name | model_name | revenue

I’m trying this query below. I need to bring the country/models that do not have any sales too with a revenue of 0, but my query only return the country/models that have any sales.

SELECT c.name as country_name,
       m.name as model_name, 
       IFNULL(SUM(s.quantity * m.price),0) as revenue 
    FROM
    sales s
     right join model m on s.model_id = m.id
     right join country c on s.country_id = c.id
where date(s.sales_date) between '2017-01-01' and '2017-12-31'    
group by c.id, m.id
order by c.id, m.id;

Result of the query

Brazil  ZTX100  50000
Italy   AHT567  120000
China   JPF090  210000

What i really need (the order is not important)

Brazil  ZTX100  50000
Brazil  AHT567  0
Brazil  JPF090  0

Italy   ZTX100  0
Italy   AHT567  120000
Italy   JPF090  0

China   ZTX100  0
China   AHT567  0
China   JPF090  210000

There is a simple way to do that?

Answer

You can cross join the countries and model table to generate all possible combinations, and then bring in the sales with a left join:

SELECT 
    c.name as country_name,
    m.name as model_name, 
    IFNULL(SUM(s.quantity * m.price),0) as revenue 
FROM 
    country c
    cross join model m
    left join sales s
        on s.model_id = m.id
        and s.country_id = c.id
        and s.sales_date >= '2017-01-01' 
        and s.sales_date <  '2018-01-01'    
group by c.id, m.id, c.name, m.name
order by c.id, m.id;

Note that I did the following changes in the query:

• use half-open intervals for the date comparison; this will be more efficient, since no date function needs to be applied on sales_date

• add all non-aggregated columns to the group by clause, making the query compliant with MySQL mode ONLY_FULL_GROUP_BY, which is enabled by default starting MySQ 5.7