Mysql SELECT with column using subquery and a IN

Question

I have a field named category_id from my table contact with as content, an id or a list ids of categories (1 or 1,2,3 ) per contact .

Name of the categories coming from the category table who have id and name column.

I like to display the result of all categories name coming from the categories list from the contact table. How to do that ?

SELECT c.`id`,
    (SELECT cat.`name` 
     FROM category cat 
     WHERE c.`category` in cat.`id` ) AS 'Categories'
FROM contact c

I tested this, but of course it's not working. The c. category column content can be 1,2,3 or 3 .

Answer 1

Your have a category field which contains the literal text 1,2,3 ? Then what you want is not directly possible. Fields are considered atomic entities in SQL, and your query is being parsed/executed as

WHERE c.category IN ('1,2,3')
aka
WHERE c.category = '1,2,3'

Instead of the

WHERE c.category IN ('1', '2', '3')
aka
WHERE (c.category = '1') OR (c.category = '2') OR (c.category = '3')

you're needing.

MySQL does have FIND_IN_SET() for this sort of thing, but note that using it prevents use of indexes and your query performance will be crap on any largeish tables. It also renders your SQL non-portable.

Answer 2

SELECT con.`id`, cat.'name'
FROM contract con
INNER JOIN category cat ON con.'category' = cat.'id'
WHERE c.category IN ('1,2,3')

Answer 3

SELECT c.`id`, cat.'name'
FROM contract c
RIGHT JOIN category cat ON c.'category' = cat.'id'
WHERE c.category IN ('1,2,3')