fix select_limited_ids_list issues in postgresql, retain current behavior in other adapters [Rick]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5291 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

1 files changed, 10 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index a2eaac549e..975768a758 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -186,7 +186,6 @@ module ActiveRecord
         execute "ROLLBACK"
       end
 
-
       # SCHEMA STATEMENTS ========================================
 
       # Return the list of all tables in the schema search path.
@@ -384,6 +383,16 @@ module ActiveRecord
           'bigint'
         end
       end
+      
+      # PostgreSQL requires the ORDER BY columns in the select list for distinct queries.
+      # If you select distinct by a column though, you must pass that column in the order by clause too:
+      #
+      #   distinct("posts.id", 'posts.id', 'posts.created_at')
+      def distinct(columns, *order_columns)
+        order_columns.delete_if &:blank?
+        sql = "DISTINCT ON (#{columns}) #{columns}"
+        sql << (order_columns.any? ? ", #{order_columns * ', '}" : '')
+      end
 
       private
         BYTEA_COLUMN_TYPE_OID = 17