conflict_target

# File activerecord/lib/active_record/insert_all.rb, line 161
        def conflict_target
          if index = insert_all.unique_by
            sql = +"(#{format_columns(index.columns)})"
            sql << " WHERE #{index.where}" if index.where
            sql
          elsif update_duplicates?
            "(#{format_columns(insert_all.primary_keys)})"
          end
        end