Fix FinderMethods#last unscoped primary key

Fixes table.joins(:relation).last(N) breaking on sqlite

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/test/cases/finder_test.rb

3 files changed, 21 insertions, 2 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 5abc84d3fb..5651783092 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,4 +1,9 @@
 ## unreleased ##
+*   Fix `FinderMethods#last` unscoped primary key.
+
+    Fixes #11917.
+
+    *Eugene Kalenkovich*
 
 *   Load fixtures from linked folders.
 
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index cdf18f8080..1efe4dbfde 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -134,8 +134,8 @@ module ActiveRecord
     def last(*args)
       if args.any?
         if args.first.kind_of?(Integer) || (loaded? && !args.first.kind_of?(Hash))
-          if order_values.empty?
-            order("#{primary_key} DESC").limit(*args).reverse
+          if order_values.empty? && primary_key
+            order("#{quoted_table_name}.#{quoted_primary_key} DESC").limit(*args).reverse
           else
             to_a.last(*args)
           end
diff --git a/activerecord/test/cases/finder_test.rb b/activerecord/test/cases/finder_test.rb
index 2efafe5c24..89e17643f6 100644
--- a/activerecord/test/cases/finder_test.rb
+++ b/activerecord/test/cases/finder_test.rb
@@ -305,10 +305,24 @@ class FinderTest < ActiveRecord::TestCase
     assert_sql(/LIMIT 5|ROWNUM <= 5/) { Topic.last(5).entries }
   end
 
+  def test_last_should_use_default_order
+    assert_sql(/ORDER BY .topics.\..id. DESC/) { Topic.last }
+  end
+
+  def test_last_with_integer_should_use_default_order
+    assert_sql(/ORDER BY .topics.\..id. DESC/) { Topic.last(5).entries }
+  end
+
   def test_last_with_integer_and_order_should_keep_the_order
     assert_equal Topic.order("title").to_a.last(2), Topic.order("title").last(2)
   end
 
+  def test_last_with_integer_should_work_with_joins
+    assert_nothing_raised do
+      Post.joins(:comments).last(2)
+    end
+  end
+
   def test_last_with_integer_and_order_should_not_use_sql_limit
     query = assert_sql { Topic.order("title").last(5).entries }
     assert_equal 1, query.length