ruby-on-rails – Rails ActiveRecord Model.uniq.pluck：id不适用于postgres

我有一个空的demo rails 4 app尝试执行以下操作：Collection.order(‘created_at ASC’).uniq.pluck：name它在sqlite下工作,但在postgres中爆炸,出现以下错误：

(0.9ms)  SELECT disTINCT "collections"."name" FROM "collections" ORDER BY created_at ASC
PG::Error: ERROR:  for SELECT disTINCT,ORDER BY expressions must appear in select list
LINE 1: ...collections"."name" FROM "collections"   ORDER BY created_at...

这是一个错误或我该如何解决？

解决方法

这似乎是Postgresql的一个问题. ( Rails 3 DISTINCT QUERY)

要解决它,您可以使用select代替：

Collection.select([：name,：created_at]).order(‘created_at ASC’).uniq.select(：name)

或者你可以让Ruby获得唯一的名称而不是sql：

Collection.order(‘created_at ASC’).pluck(：name).uniq