Fix `COUNT(DISTINCT ...)` for `GROUP BY` with `ORDER BY` and `LIMIT`

This is the fix for the regression of #29848.

In #29848, I've kept existing select list in the subquery for the count
if ORDER BY is given. But it had accidentally affect to GROUP BY
queries also. It should keep the previous behavior in that case.

Fixes #30886.

1 files changed, 4 insertions, 0 deletions

diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index b47fd0af41..66bc14b5ab 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -260,6 +260,10 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal 3, Account.joins(:firm).distinct.order(:firm_id).limit(3).offset(2).count
   end
 
+  def test_distinct_count_with_group_by_and_order_and_limit
+    assert_equal({ 6 => 2 }, Account.group(:firm_id).distinct.order("1 DESC").limit(1).count)
+  end
+
   def test_should_group_by_summed_field_having_condition
     c = Account.group(:firm_id).having("sum(credit_limit) > 50").sum(:credit_limit)
     assert_nil        c[1]