fix PG typecasting errors

activerecord/lib/active_record/relation/calculations.rb

@@ -241,13 +241,16 @@ def execute_simple_calculation(operation, column_name, distinct) #:nodoc:
 
         select_value = operation_over_aggregate_column(column, operation, distinct)
 
+        column_name = select_value.alias
         relation.select_values = [select_value]
 
         query_builder = relation.arel
       end
 
-      result = @klass.connection.select_value(query_builder, nil, relation.bind_values)
-      type_cast_calculated_value(result, column_for(column_name), operation)
+      result = @klass.connection.select_all(query_builder, nil, relation.bind_values)
+      row   = result.first
+      value = row && row.values.first
+      type_cast_calculated_value(value, result.column_types[column_name], operation)
     end
 
     def execute_grouped_calculation(operation, column_name, distinct) #:nodoc:

activerecord/test/cases/calculations_test.rb

@@ -8,6 +8,7 @@
 require 'models/topic'
 require 'models/minivan'
 require 'models/speedometer'
+require 'models/ship_part'
 
 Company.has_many :accounts
 
@@ -33,8 +34,9 @@ def test_should_return_decimal_average_of_integer_field
   end
 
   def test_should_return_integer_average_if_db_returns_such
-    Account.connection.stubs :select_value => 3
-    value = Account.average(:id)
+    ShipPart.delete_all
+    ShipPart.create!(:id => 3, :name => 'foo')
+    value = ShipPart.average(:id)
     assert_equal 3, value
   end
 
@@ -416,34 +418,19 @@ def test_maximum_with_from_option
   def test_maximum_with_not_auto_table_name_prefix_if_column_included
     Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
 
-    # TODO: Investigate why PG isn't being typecast
-    if current_adapter?(:PostgreSQLAdapter) || current_adapter?(:MysqlAdapter)
-      assert_equal "7", Company.includes(:contracts).maximum(:developer_id)
-    else
-      assert_equal 7, Company.includes(:contracts).maximum(:developer_id)
-    end
+    assert_equal 7, Company.includes(:contracts).maximum(:developer_id)
   end
 
   def test_minimum_with_not_auto_table_name_prefix_if_column_included
     Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
 
-    # TODO: Investigate why PG isn't being typecast
-    if current_adapter?(:PostgreSQLAdapter) || current_adapter?(:MysqlAdapter)
-      assert_equal "7", Company.includes(:contracts).minimum(:developer_id)
-    else
-      assert_equal 7, Company.includes(:contracts).minimum(:developer_id)
-    end
+    assert_equal 7, Company.includes(:contracts).minimum(:developer_id)
   end
 
   def test_sum_with_not_auto_table_name_prefix_if_column_included
     Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
 
-    # TODO: Investigate why PG isn't being typecast
-    if current_adapter?(:MysqlAdapter) || current_adapter?(:PostgreSQLAdapter)
-      assert_equal "7", Company.includes(:contracts).sum(:developer_id)
-    else
-      assert_equal 7, Company.includes(:contracts).sum(:developer_id)
-    end
+    assert_equal 7, Company.includes(:contracts).sum(:developer_id)
   end