MySQL to Postgres group_by error

Question

The following query works fine in MySQL (which is generated by rails ):

SELECT
   sum(up_votes) total_up_votes 
FROM
   "answers" 
WHERE
   "answers"."user_id" = 100
ORDER BY
   "answers"."id" ASC

Yet it gives the following error in Postgres:

PG::GroupingError: ERROR:  column "answers.id" must appear in the GROUP BY clause or be used in an aggregate function

Edit: updated query. And here is the Rails model where this query is performed:

class User < MyModel
  def top?
    data = self.answers.select("sum(up_votes) total_up_votes").first
    return (data.total_up_votes.present? && data.total_up_votes >= 10)
  end
end

Answer 1

The query may execute in MySQL, but I doubt that it "works fine". It returns only one row, so the ordering is meaningless.

Your question is vague on what you actually want to do, but this should produce the same results as your query, in both databases:

SELECT sum(up_votes) as total_up_votes
FROM answers
WHERE user_id = 100;