class ActiveRecord::Relation::Merger

def merge_clauses
  relation.from_clause = other.from_clause if replace_from_clause?
  where_clause = relation.where_clause.merge(other.where_clause, @rewhere)
  relation.where_clause = where_clause unless where_clause.empty?
  having_clause = relation.having_clause.merge(other.having_clause)
  relation.having_clause = having_clause unless having_clause.empty?
end