ORDER BY items must appear in the select list if SELECT DISTINCT is specified

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4 Tests Failing

HasAndBelongsToManyAssociationsTest#test_has_and_belongs_to_many
FinderTest#test_exists_with_distinct_association_includes_and_limit
FinderTest#test_exists_with_distinct_association_includes_limit_and_order
FinderTest#test_exists_with_order

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This quasi relates to #306 when work was done 4.0 and 4.1. Since we now use OFFSET & FETCH for our windowing strategy, we were able to directly copy the PostgreSQL implementation for the columns_for_distinct method and passed 18 tests right away.

def columns_for_distinct(columns, orders)
  order_columns = orders.reject(&:blank?).map{ |s|
      s = s.to_sql unless s.is_a?(String)
      s.gsub(/\s+(?:ASC|DESC)\b/i, '')
       .gsub(/\s+NULLS\s+(?:FIRST|LAST)\b/i, '')
    }.reject(&:blank?).map.with_index { |column, i| "#{column} AS alias_#{i}" }
  [super, *order_columns].join(', ')
end

I had considered using FIRST_VALUE and this Pinal Dave covers the topic really well. Reference the other issue if we want to explore switching over but it would likely require order hacks as the Oracle visitor has done too.