Question

So I have this query that works perfectly:

SELECT users.*,
GROUP_CONCAT(categories.category_name) AS categories
FROM users
LEFT OUTER JOIN user_categories ON users.user_id = user_categories.user_id
LEFT OUTER JOIN categories ON user_categories.category_id = categories.category_id
WHERE users.user_city = 'brooklyn'
GROUP BY users.user_id
LIMIT 10;

Say I have another table that holds phone numbers, for the “users” a user can have any number of phone numbers… How would I go about doing round about the exact same thing I am doing wit the categories? In other words, I would like to get another column with ALL of the phone_numbers found in the “phones” table that have the same “user_id” and concat them together(phone1, phone2, phone3)? I have tried:

SELECT users.*,
GROUP_CONCAT(phones.phone_number) AS phone_numbers,
GROUP_CONCAT(categories.category_name) AS categories
FROM users
LEFT OUTER JOIN phones ON users.user_id = phones.user_id
LEFT OUTER JOIN user_categories ON users.user_id = user_categories.user_id
LEFT OUTER JOIN categories ON user_categories.category_id = categories.category_id
WHERE users.user_city = 'brooklyn'
GROUP BY users.user_id
LIMIT 10;

With no luck… or at least the query executes but it does some weird duplication thing… any help would be awesome!

Thanks!

Answer 1

It does weird things, becaue there is a cross product of certain rows. You can use the DISTINCT keyword to get only unique phone numbers:

GROUP_CONCAT(DISTINCT phones.phone_number) AS phone_numbers,

Check the documentation. Alternatively, you can get the phone numbers in another query where you would select only the phone numbers with a condition like WHERE phones.user_id IN (x, x, x, ...) (x are IDs returned from the first query).