ruby on rails - PostgreSQL - must appear in the GROUP BY clause or be used in an aggregate function -

this query works locally, doesn't work on heroku reason.

2014-06-26t00:45:11.334388+00:00 app[web.1]: pg::groupingerror: error:  column  "conversations.updated_at" must appear in group clause or used in  aggregate  function 

this sql.

conversation.joins("inner join notifications on  notifications.conversation_id = conversations.id ,  notifications.type in ('message') inner join receipts  on receipts.notification_id =  notifications.id  notifications.type = 'message' , (receipts.receiver_id = #{a.id}  , receipts.receiver_type = 'profile') , conversations.id  in #{active_conversations_ids} order conversations.updated_at desc") 

i tried doing distinct , did not work, , tried group_by('conversation_id')

the to_sql

select "conversations".* "conversations" inner join  notifications on notifications.conversation_id = conversations.id  , notifications.type in ('message') inner join receipts  on receipts.notification_id =  notifications.id notifications.type = 'message' , (receipts.receiver_id = 104  , receipts.receiver_type = 'profile') , conversations.id  in (…) order conversations.updated_at desc" 

you can see sql in server window, if running app in local machine.

it practice keep joins belong to.

conversation.where('id' => active_conversations_ids).joins( "inner join notifications on notifications.conversation_id = conversations.id    , notifications.type in ('message')  inner join receipts on receipts.notification_id = notifications.id    , (receipts.receiver_id = #{a.id} , receipts.receiver_type = 'profile')" ).order('updated_at') 

and better readability, can use notifications symbols.

conversation .find_all_by_id(active_conversations_ids) .joins(:notifications, :receipts).where({        notifications: { type: 'message' },      receipts: { receiver_id: a.id, receiver_type: 'profile'} }) .order('updated_at') 

my final suggestion google named scopes.

http://zachholman.com/2010/01/simplifying-rails-controllers-with-named_scopes/