2 files changed, 16 insertions, 5 deletions
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index 862009b1ba..aa9f7b71bf 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -140,19 +140,26 @@ module ActiveRecord
     #   # => ['0', '27761', '173']
     #
     def pluck(column_name)
-      key = column_name.to_s.split('.', 2).last
-
       if column_name.is_a?(Symbol) && column_names.include?(column_name.to_s)
         column_name = "#{table_name}.#{column_name}"
       end
 
       result = klass.connection.select_all(select(column_name).arel, nil, bind_values)
-      column = klass.column_types[key] || result.column_types.values.first
+
+      key = column = nil
+      nullcast = Class.new { def type_cast(v); v; end }.new
 
       result.map do |attributes|
         raise ArgumentError, "Pluck expects to select just one attribute: #{attributes.inspect}" unless attributes.one?
+
         value = klass.initialize_attributes(attributes).values.first
-        column ? column.type_cast(value) : value
+
+        key    ||= attributes.keys.first
+        column ||= klass.column_types.fetch(key) {
+          result.column_types.fetch(key, nullcast)
+        }
+
+        column.type_cast(value)
       end
     end
 
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index f8bd11e3d0..041f8ffb7c 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -470,7 +470,11 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal [50, 53, 55, 60], Account.pluck('DISTINCT credit_limit').sort
     assert_equal [50, 53, 55, 60], Account.pluck('DISTINCT accounts.credit_limit').sort
     assert_equal [50, 53, 55, 60], Account.pluck('DISTINCT(credit_limit)').sort
-    assert_equal [50 + 53 + 55 + 60], Account.pluck('SUM(DISTINCT(credit_limit))')
+
+    # MySQL returns "SUM(DISTINCT(credit_limit))" as the column name unless
+    # an alias is provided.  Without the alias, the column cannot be found
+    # and properly typecast.
+    assert_equal [50 + 53 + 55 + 60], Account.pluck('SUM(DISTINCT(credit_limit)) as credit_limit')
   end
 
   def test_pluck_expects_a_single_selection