I have a database with a table for publications, each of which can have multiple authors that are stored in a different table. I'd like to query the database into giving me a list of publication titles in one column, and the combined authors for that publication in the second.
SELECT p.`id`, p.`title`, a.`fullname`
from `publications` p
LEFT JOIN `authors` a on a.`publication_id` = p.`id`;
This of course gives me multiple times the publication title for as many authors.
id title fullname
-- ----- --------
1 Beneath the Skin Sean French
1 Beneath the Skin Nicci Gerrard
2 The Talisman Stephen King
2 The Talisman Peter Straub
Grouping on id gives me one author per title:
SELECT p.`id`, p.`title`, a.`fullname`
from `publications` p
LEFT JOIN `authors` a on a.`publication_id` = p.`id`
GROUP BY a.`id`;
id title fullname
-- ----- --------
1 Beneath the Skin Sean French
2 The Talisman Stephen King
The result I'm looking for is this:
id title fullname
-- ----- --------
1 Beneath the Skin Sean French, Nicci Gerrard
2 The Talisman Stephen King, Peter Straub
I think the answer should be found in using GROUP_CONCAT, but the only result I'm able to get is one result row with all authors:
SELECT p.`id`, p.`title`, GROUP_CONCAT(a.`fullname`) from `publications` p
LEFT JOIN `authors` a on a.`publication_id` = p.`id`
GROUP BY a.`id`;
id title fullname
-- ----- --------
1 Beneath the Skin Sean French, Nicci Gerrard, Stephen King, Peter Straub
And using GROUP_CONCAT after the join gives me an "Every derived table must have its own alias" error.
SELECT p.`id`, p.`title`, a.`fullname`
FROM `publications` p
LEFT JOIN (SELECT GROUP_CONCAT(a.`fullname`) FROM `authors` a) ON a.`publication_id` = p.`id`;
Any clues?
You need to group by all of the non-aggregated columns in the SELECT (and explicitly, not group by the author id, because author is part of the GROUP_CONCAT):
SELECT p.`id`, p.`title`, GROUP_CONCAT(a.`fullname` separator ', ')
from `publications` p
LEFT JOIN `authors` a on a.`publication_id` = p.`id`
GROUP BY p.`id`, p.`title`;