Fix `count(:all)` with eager loading and having an order other than the driving table

This is a regression caused by 6beb4de.

In PostgreSQL, ORDER BY expressions must appear in SELECT list when
using DISTINCT.

When using `count(:all)` with eager loading, Active Record enforces
DISTINCT to count the driving table records only. 6beb4de was caused the
regression because `count(:all)` with DISTINCT path no longer removes
ORDER BY.

We need to ignore ORDER BY when DISTINCT is enforced, otherwise not
always generated valid SQL for PostgreSQL.

Fixes #31783.

1 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 19489f3c71..673ff95bc2 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -969,6 +969,12 @@ class RelationTest < ActiveRecord::TestCase
     assert_queries(1) { assert_equal 8, posts.load.size }
   end
 
+  def test_size_with_eager_loading_and_custom_order
+    posts = Post.includes(:comments).order("comments.id")
+    assert_queries(1) { assert_equal 11, posts.size }
+    assert_queries(1) { assert_equal 11, posts.load.size }
+  end
+
   def test_update_all_with_scope
     tag = Tag.first
     Post.tagged_with(tag.id).update_all title: "rofl"