method

distinct

v2.2.1 - Show latest stable - Class: ActiveRecord::ConnectionAdapters::PostgreSQLAdapter

distinct(columns, order_by)

public

Returns a SELECT DISTINCT clause for a given set of columns and a given ORDER BY clause.

PostgreSQL requires the ORDER BY columns in the select list for distinct queries, and requires that the ORDER BY include the distinct column.

  distinct("posts.id", "posts.created_at desc")

# File activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb, line 884
      def distinct(columns, order_by) #:nodoc:
        return "DISTINCT #{columns}" if order_by.blank?

        # Construct a clean list of column names from the ORDER BY clause, removing
        # any ASC/DESC modifiers
        order_columns = order_by.split(',').collect { |s| s.split.first }
        order_columns.delete_if &:blank?
        order_columns = order_columns.zip((0...order_columns.size).to_a).map { |s,i| "#{s} AS alias_#{i}" }

        # Return a DISTINCT ON() clause that's distinct on the columns we want but includes
        # all the required columns for the ORDER BY to work properly.
        sql = "DISTINCT ON (#{columns}) #{columns}, "
        sql << order_columns * ', '
      end

distinct

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