MySQL 5.6

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select version();


version()


5.6.51


CREATE TABLE users
(
  user_id INTEGER NOT NULL PRIMARY KEY,
  u_date  DATE NOT NULL,
  country VARCHAR (100) NOT NULL
);
CREATE TABLE submissions
(
  submission_id   INTEGER PRIMARY KEY,
  user_id         INTEGER NOT NULL,
  submission_date DATE,
  category        VARCHAR (100) NOT NULL,
  CONSTRAINT sub_user_fk FOREIGN KEY (user_id) REFERENCES users (user_id)
);
INSERT INTO users VALUES
(123, '2022-12-01', 'USA'),
(124, '2022-12-01', 'Ireland'),
(125, '2022-12-01', 'Japan');
INSERT INTO submissions VALUES
( 1, 123, '2022-12-02', 'business'),
( 2, 123, '2022-12-02', 'business'),
( 3, 123, '2022-12-02',  'tourism'),
( 4, 123, '2022-12-02',  'tourism'),
( 5, 123, '2022-12-02',  'tourism'),
( 6, 124, '2022-12-02', 'business'),
( 7, 124, '2022-12-02',  'tourism');

--
-- Note: no records in submissions for user 125
--
SELECT 
  u.user_id, u.country, s.category, 
  COUNT(s.category) AS cat_cnt
FROM
  users u
INNER JOIN
  submissions s
  ON u.user_id = s.user_id
GROUP BY u.user_id, u.country, s.category
ORDER BY u.user_id, u.country;


user_id
country
category
cat_cnt


123
USA
business
2

123
USA
tourism
3

124
Ireland
business
1

124
Ireland
tourism
1


SELECT 
  u.user_id, u.country, COALESCE(s.category, '------'), 
  COUNT(s.category) AS cat_cnt
FROM
  users u
LEFT JOIN
  submissions s
  ON u.user_id = s.user_id
GROUP BY u.user_id, u.country, s.category
ORDER BY u.user_id, u.country;


user_id
country
COALESCE(s.category, '------')
cat_cnt


123
USA
business
2

123
USA
tourism
3

124
Ireland
business
1

124
Ireland
tourism
1

125
Japan
------
0


SELECT country, category, count(1) FROM users u 
   JOIN submissions s ON u.user_id= s.user_id GROUP BY country, category


country
category
count(1)


Ireland
business
1

Ireland
tourism
1

USA
business
2

USA
tourism
3


SELECT country, category, count(country) FROM users u 
   JOIN submissions s ON u.user_id= s.user_id GROUP BY country, category


country
category
count(country)


Ireland
business
1

Ireland
tourism
1

USA
business
2

USA
tourism
3


INSERT INTO users VALUES
(126, '2022-12-01', 'USA');
INSERT INTO submissions VALUES
( 8, 126, '2022-12-02',  'tourism'),
( 9, 126, '2022-12-02',  'tourism'),
(10, 126, '2022-12-02',  'tourism'),
(11, 126, '2022-12-02', 'business'),
(12, 126, '2022-12-02', 'business');
SELECT 
  u.country, COALESCE(s.category, '------') AS category, 
  COUNT(s.category) AS cat_cnt
FROM
  users u
LEFT JOIN
  submissions s
  ON u.user_id = s.user_id
GROUP BY u.country, s.category
ORDER BY u.country, category DESC, s.category;


country
category
cat_cnt


Ireland
tourism
1

Ireland
business
1

Japan
------
0

USA
tourism
6

USA
business
4
user_id	country	category	cat_cnt
123	USA	business	2
123	USA	tourism	3
124	Ireland	business	1
124	Ireland	tourism	1