fixes different `count` calculation when using `size` manual `select` with DISTINCT

When using `select` with `'DISTINCT( ... )'` if you use method `size` on a non loaded relation it overrides the column selected by passing `:all` so it returns different value than count.

This fixes #35214

2 files changed, 25 insertions, 0 deletions

diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index 8ac2d55218..840920ccb6 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -473,6 +473,24 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal 6, Account.select("DISTINCT accounts.id").includes(:firm).count
   end
 
+  def test_should_count_manual_select_with_count_all
+    assert_equal 5, Account.select("DISTINCT accounts.firm_id").count(:all)
+  end
+
+  def test_should_count_with_manual_distinct_select_and_distinct
+    assert_equal 4, Account.select("DISTINCT accounts.firm_id").distinct(:id).count
+  end
+
+  def test_should_count_manual_select_with_group_with_count_all
+    expected = { nil => 1, 1 => 1, 2 => 1, 6 => 2, 9 => 1 }
+    actual = Account.select("DISTINCT accounts.firm_id").group("accounts.firm_id").count(:all)
+    assert_equal expected, actual
+  end
+
+  def test_should_count_manual_with_count_all
+    assert_equal 6, Account.count(:all)
+  end
+
   def test_count_selected_arel_attribute
     assert_equal 5, Account.select(Account.arel_table[:firm_id]).count
     assert_equal 4, Account.distinct.select(Account.arel_table[:firm_id]).count
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 2de0a81c99..5a3bd1bd4a 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -972,6 +972,13 @@ class RelationTest < ActiveRecord::TestCase
     assert_queries(1) { assert_equal 11, posts.load.size }
   end
 
+  def test_size_with_eager_loading_and_manual_distinct_select_and_custom_order
+    accounts = Account.select("DISTINCT accounts.firm_id").order("accounts.firm_id")
+
+    assert_queries(1) { assert_equal 5, accounts.size }
+    assert_queries(1) { assert_equal 5, accounts.load.size }
+  end
+
   def test_count_explicit_columns
     Post.update_all(comments_count: nil)
     posts = Post.all