MySQL 5.7

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CREATE TABLE user
    (`user_id` int, `name` varchar(5))
;
    
INSERT INTO user
    (`user_id`, `name`)
VALUES
    (1, 'Bob'),
    (2, 'Tim'),
    (3, 'Dave'),
    (4, 'Simon'),
    (5, 'Ben')
;


CREATE TABLE user_category
    (`user_id` int, `category_id` int)
;
    
INSERT INTO user_category
    (`user_id`, `category_id`)
VALUES
    (1, 1),
    (1, 5),
    (1, 3),
    (2, 4),
    (2, 1),
    (3, 2),
    (3, 4),
    (4, 4),
    (4, 1),
    (5, 3),
    (5, 5)
;


CREATE TABLE category
    (`category_id` int, `category` varchar(8))
;
    
INSERT INTO category
    (`category_id`, `category`)
VALUES
    (1, 'drawing'),
    (2, 'climbing'),
    (3, 'hunting'),
    (4, 'fishing'),
    (5, 'sleeping')
;
SELECT category_id,Count(*) FROM user_category Group By category_id;


category_id
Count(*)


1
3

2
1

3
2

4
3

5
2


SELECT MIN(c.category),Count(*),GROUP_CONCAT(`name`)
FROM user_category uc  
inner join user u ON uc.user_id = u.user_id 
inner join category c on uc.category_id = c.category_id
GROUP BY uc.category_id


MIN(c.category)
Count(*)
GROUP_CONCAT(`name`)


drawing
3
Bob,Tim,Simon

climbing
1
Dave

hunting
2
Bob,Ben

fishing
3
Tim,Dave,Simon

sleeping
2
Bob,Ben

MIN(c.category)	Count(*)	GROUP_CONCAT(`name`)
drawing	3	Bob,Tim,Simon
climbing	1	Dave
hunting	2	Bob,Ben
fishing	3	Tim,Dave,Simon
sleeping	2	Bob,Ben