PG:GroupingError only appearing on production - sql

Question

I have a model "Playlist" which has_many and belongs_to another model "User", through an intermediary model "PlaylistUser".
I have code that, for a given Playlist #playlist, lists all the other Playlists that share a User with #playlist, ordered by how many they share.
This code works perfectly on development, but on production, it's throwing this error:
PG::GroupingError: ERROR: column "playlists.name" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT "playlists".* FROM "playlists" INNER JOIN "playlist...
^
: SELECT "playlists".* FROM "playlists" INNER JOIN "playlist_users" ON "playlist_users"."playlist_id" = "playlists"."id" INNER JOIN "users" ON "users"."id" = "playlist_users"."user_id" WHERE (NOT (playlists.id = 30 OR playlists.id = 41)) AND "users"."id" IN (45, 89, 71, 117, 115, 173, 177, 180, 161, 220, 223, 199, 221, 239, 204, 205, 206, 207, 211, 261, 282, 284, 286, 251, 252, 255, 310, 311, 315, 318, 307, 362, 319, 306, 289, 316, 305, 321, 322, 330, 333, 292, 294, 304, 300, 340, 341, 342, 343, 405, 406, 410, 408, 409, 407, 413, 416, 417, 418, 425, 427, 392, 401, 403, 445, 446, 449, 450, 379, 456, 451, 454, 459, 437, 442, 444, 496, 501, 518, 548, 549, 533, 553, 1112, 1113, 1459, 455, 348, 1458, 242, 1275, 151, 1890, 336, 203, 404, 166, 453, 114, 157, 285, 448, 447, 443, 550, 2167, 2168, 287, 320, 293, 65, 2098, 2097, 2099, 387, 3, 2175, 2170, 2174, 2182, 2171, 438, 2180, 2181, 2169, 2176, 347, 2429, 2177, 2445, 2178, 2447, 58, 2480, 390, 452, 554, 555, 313, 92, 275, 335, 428, 167, 302, 2173, 1538) GROUP BY playlists.id ORDER BY count(*) desc
Why would my query be working on development but not on production?
Query
#playlist_ids = #playlist.user_ids
#more_playlists = Playlist.joins(:users).where.not('playlists.id = ? OR playlists.id = ?', 30, 41).where(users: {id: #playlist_ids}).group('playlists.id').order('count(*) desc')
Assocations:
class Playlist < ActiveRecord::Base
has_many :playlist_users
has_many :users, :through => :playlist_users
end
class PlaylistUser < ActiveRecord::Base
belongs_to :playlist
belongs_to :user
end
class User < ActiveRecord::Base
has_many :playlist_users
has_many :playlists, :through => :playlist_users
end
UPDATE
This is pretty strange, I added Playlist.name to the GROUP BY as per trincot's suggestion:
#playlist_ids = #playlist.user_ids
Playlist.select('playlists.id, playlists.name')
.joins(:playlist_users)
.where('playlists.id NOT IN (30, 41)')
.where(playlist_users: {user_id: #playlist_ids})
.group('playlists.id, playlists.name')
.order('count(*) desc')
But I'm getting back a similar error, except now it's telling me I have to include thePlaylist attribute subject_id in the GROUP BY clause:
PG::GroupingError: ERROR: column "playlists.subject_id" must appear in the GROUP BY clause or be used in an aggregate function
But I didn't reference subject_id literally anywhere in my query, or even in the model, controller, or view for the page. Why on earth would that column even be involved in this?

Answer 1

Your statement is not valid according to the PostgreSQL documentation:
When GROUP BY is present, it is not valid for the SELECT list expressions to refer to
ungrouped columns except within aggregate functions, since there would be more than one
possible value to return for an ungrouped column.
If you say it works in your development environment, it must mean that environment has another database engine (version) running.
You should use a statement like this, where the list of fields in the SELECT clause is the same as the list given in the GROUP BY clause:
SELECT playlists.id, playlists.name, ...
FROM playlists
INNER JOIN playlist_users ON playlist_users.playlist_id = playlists.id
WHERE playlists.id NOT IN (30, 41)
AND playlist_users.user_id IN (your_long_list_comes_here)
GROUP BY playlists.id, playlists.name, ...
ORDER BY count(*) desc
Note that you don't actually need to join the users table for the result of your interest, so I removed it and replaced the test on user_id accordingly. Also, the condition on the playlists.id is expressed more concise using the IN operator.
The corresponding Active Record query would be:
Playlist.joins(:playlist_users)
.where('playlists.id NOT IN (30, 41)')
.where(playlist_users: {user_id: #playlist_ids})
.select('playlists.id, playlists.name')
.group('playlists.id, playlists.name')
.order('count(*) desc')
You have to add any other fields you need in both the select and group arguments.