incompatible with sql_mode=only_full_group_by in mysql

Question

So while upgrading a project from Rails 3.2 to Rails 4.2, somehow this query in one of my models which looks like:

rows = ActiveRecord::Base.connection.execute("Select q.id,q.times_taken,avg(qr.correct)*100,q.difficulty,q.weight,sk.name,sa.name,sub.name,q.tag_list from 
  (select qu.id,qu.times_taken,qu.difficulty,qu.weight,group_concat(tags.name) tag_list,qu.subject_id,qu.subject_area_id
    from questions qu left join taggings t on (qu.id = taggable_id) left join tags on (t.tag_id = tags.id) 
    where qu.id in (#{@questions_out_ids.join(',')}) and t.taggable_type='Question' group by t.taggable_id) q
  left join subjects sub on (q.subject_id = sub.id) left join subject_areas sa on (q.subject_area_id = sa.id) 
  left join skills_subject_areas ssa on (sa.id = ssa.subject_area_id) left join skills sk on (ssa.skill_id = sk.id), 
  archived_question_results qr,attempts a where  qr.question_id = q.id and a.id = qr.attempt_id and a.is_normalized = 1 
  and a.state = 'complete' group by qr.question_id order by q.id")

has started producing a mysql error as under:

ERROR 1055 (42000): Expression #6 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'faces_development.sk.name' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

I've looked at other answers of the similar questions, and I know I need to include a certain table's id column too in the GROUP BY clause but since my query is extremely complex, the options I've tried haven't been of much use. I am using gem mysql2 0.3.0 Suggestions ?

Answer 1

config/database.yml:

development: # Or test, or production, or all of them.
  ...
  variables:
    sql_mode: TRADITIONAL

Answer 2

in your config/database.yml file:

default: &default
  variables:
    sql_mode: TRADITIONAL