Fix type cast on group sum with custom expression

For PG adapters with custom expression and grouped result
of aggregate functions have not found correct column type
for it. Extract column type from query result.

Closes: #13230

3 files changed, 23 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 4222308f8b..af1d192daa 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,19 @@
+*   Use the right column to type cast grouped calculations with custom expressions.
+
+    Fixes: #13230
+
+    Example:
+
+            # Before
+            Account.group(:firm_name).sum('0.01 * credit_limit')
+            # => { '37signals' => '0.5' }
+
+            # After
+            Account.group(:firm_name).sum('0.01 * credit_limit')
+            # => { '37signals' => 0.5 }
+
+    *Paul Nikitochkin*
+
 *   Polymorphic `belongs_to` associations with the `touch: true` option set update the timestamps of
     the old and new owner correctly when moved between owners of different types.
 
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index 2d267183ce..cf24d10a8d 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -311,7 +311,9 @@ module ActiveRecord
         }
         key = key.first if key.size == 1
         key = key_records[key] if associated
-        [key, type_cast_calculated_value(row[aggregate_alias], column_for(column_name), operation)]
+
+        column_type = calculated_data.column_types.fetch(aggregate_alias) { column_for(column_name) }
+        [key, type_cast_calculated_value(row[aggregate_alias], column_type, operation)]
       end]
     end
 
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index 2c41656b3d..2f6913167d 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -211,6 +211,10 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal 19.83, NumericData.sum(:bank_balance)
   end
 
+  def test_should_return_type_casted_values_with_group_and_expression
+    assert_equal 0.5, Account.group(:firm_name).sum('0.01 * credit_limit')['37signals']
+  end
+
   def test_should_group_by_summed_field_with_conditions
     c = Account.where('firm_id > 1').group(:firm_id).sum(:credit_limit)
     assert_nil        c[1]