Method: ActiveRecord::ConnectionAdapters::PostgreSQLAdapter#distinct

Defined in:
lib/active_record/connection_adapters/postgresql_adapter.rb

#distinct(columns, orders) ⇒ Object

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")



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# File 'lib/active_record/connection_adapters/postgresql_adapter.rb', line 1087

def distinct(columns, orders) #:nodoc:
  return "DISTINCT #{columns}" if orders.empty?

  # Construct a clean list of column names from the ORDER BY clause, removing
  # any ASC/DESC modifiers
  order_columns = orders.collect { |s| s.gsub(/\s+(ASC|DESC)\s*/i, '') }
  order_columns.delete_if { |c| c.blank? }
  order_columns = order_columns.zip((0...order_columns.size).to_a).map { |s,i| "#{s} AS alias_#{i}" }

  "DISTINCT #{columns}, #{order_columns * ', '}"
end