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

Since #26972, `ORDER BY` is kept if `LIMIT` is presented for
performance. But in most SQL servers (e.g. PostgreSQL, SQL Server, etc),
`ORDER BY` expressions must appear in select list for `SELECT DISTINCT`.
We should not replace existing select list in that case.

1 files changed, 12 insertions, 0 deletions

diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index dd6815b149..0541b78f0f 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -236,6 +236,18 @@ class CalculationsTest < ActiveRecord::TestCase
     end
   end
 
+  def test_distinct_count_with_order_and_limit
+    assert_equal 4, Account.distinct.order(:firm_id).limit(4).count
+  end
+
+  def test_distinct_count_with_order_and_offset
+    assert_equal 4, Account.distinct.order(:firm_id).offset(2).count
+  end
+
+  def test_distinct_count_with_order_and_limit_and_offset
+    assert_equal 4, Account.distinct.order(:firm_id).limit(4).offset(2).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]