def pluck(column_name)
      column_name = column_name.to_s
      relation = clone
      relation.select_values = [column_name]
      klass.connection.select_all(relation.arel).map! do |attributes|
        klass.type_cast_attribute(attributes.keys.first, klass.initialize_attributes(attributes))
      end
    end
def pluck(column_name)
      column_name = column_name.to_s
      relation = clone
      relation.select_values = [column_name]
      klass.connection.select_all(relation.arel).map! do |attributes|
        klass.type_cast_attribute(attributes.keys.first, klass.initialize_attributes(attributes))
      end
    end
This method is designed to perform select by a single column as direct SQL query
 Returns <tt>Array</tt> with values of the specified column name
 The values has same data type as column.

 Examples:

   Person.pluck(:id) # SELECT people.id FROM people
   Person.uniq.pluck(:role) # SELECT DISTINCT role FROM people
   Person.where(:confirmed => true).limit(5).pluck(:id)