method

distinct

v1.2.6 - Show latest stable - 0 notes - Class: ActiveRecord::ConnectionAdapters::OracleAdapter

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What's this?

distinct(columns, order_by) public

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

Oracle requires the ORDER BY columns to be in the SELECT list for DISTINCT queries. However, with those columns included in the SELECT DISTINCT list, you won’t actually get a distinct list of the column you want (presuming the column has duplicates with multiple values for the ordered-by columns. So we use the FIRST_VALUE function to get a single (first) value for each column, effectively making every row the same.

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

Show source

# File activerecord/lib/active_record/connection_adapters/oracle_adapter.rb, line 464
        def distinct(columns, order_by)
          return "DISTINCT #{columns}" if order_by.blank?

          # construct a valid DISTINCT clause, ie. one that includes the ORDER BY columns, using
          # FIRST_VALUE such that the inclusion of these columns doesn't invalidate the DISTINCT
          order_columns = order_by.split(',').map { |s| s.strip }.reject(&:blank?)
          order_columns = order_columns.zip((0...order_columns.size).to_a).map do |c, i|
            "FIRST_VALUE(#{c.split.first}) OVER (PARTITION BY #{columns} ORDER BY #{c}) AS alias_#{i}__"
          end
          sql = "DISTINCT #{columns}, "
          sql << order_columns * ", "
        end

distinct

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