Fix `relation.exists?` with giving both `distinct` and `offset`

The `distinct` affects (reduces) rows of the result, so it is important
part when both `distinct` and `offset` are given.

Replacing SELECT clause to `1 AS one` and removing `distinct` and
`order` is just optimization for the `exists?`, we should not apply the
optimization for that case.

Fixes #35191.

1 files changed, 10 insertions, 0 deletions

diff --git a/activerecord/test/cases/finder_test.rb b/activerecord/test/cases/finder_test.rb
index 6af2a43c7f..4040682280 100644
--- a/activerecord/test/cases/finder_test.rb
+++ b/activerecord/test/cases/finder_test.rb
@@ -271,6 +271,16 @@ class FinderTest < ActiveRecord::TestCase
     assert_equal true, Topic.exists?({})
   end
 
+  def test_exists_with_distinct_and_offset_and_joins
+    assert Post.left_joins(:comments).distinct.offset(10).exists?
+    assert_not Post.left_joins(:comments).distinct.offset(11).exists?
+  end
+
+  def test_exists_with_distinct_and_offset_and_select
+    assert Post.select(:body).distinct.offset(3).exists?
+    assert_not Post.select(:body).distinct.offset(4).exists?
+  end
+
   # Ensure +exists?+ runs without an error by excluding distinct value.
   # See https://github.com/rails/rails/pull/26981.
   def test_exists_with_order_and_distinct