5 files changed, 35 insertions, 3 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 00ea49fa9d..dead555cca 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Fixed error for aggregate methods (`empty?`, `any?`, `count`) with `select`
+    which created invalid SQL.
+
+    Fixes #13648.
+
+    *Simon Woker*
+
 *   PostgreSQL adapter only warns once for every missing OID per connection.
 
     Fixes #14275.
diff --git a/activerecord/lib/active_record/association_relation.rb b/activerecord/lib/active_record/association_relation.rb
index 20516bba0c..ef9650d482 100644
--- a/activerecord/lib/active_record/association_relation.rb
+++ b/activerecord/lib/active_record/association_relation.rb
@@ -9,6 +9,14 @@ module ActiveRecord
       @association
     end
 
+    def size
+      @association.size
+    end
+
+    def empty?
+      @association.empty?
+    end
+
     private
 
     def exec_queries
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index 787f55e2e7..d1764a2bb2 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -238,7 +238,7 @@ module ActiveRecord
 
     # Returns size of the records.
     def size
-      loaded? ? @records.length : count
+      loaded? ? @records.length : count(:all)
     end
 
     # Returns true if there are no records.
@@ -248,8 +248,7 @@ module ActiveRecord
       if limit_value == 0
         true
       else
-        # FIXME: This count is not compatible with #select('authors.*') or other select narrows
-        c = count
+        c = count(:all)
         c.respond_to?(:zero?) ? c.zero? : c.empty?
       end
     end
diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index 8c9797861c..7eaa5adc86 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -1198,6 +1198,14 @@ class EagerAssociationTest < ActiveRecord::TestCase
     assert_equal authors(:bob), author
   end
 
+  test "preloading with a polymorphic association and using the existential predicate but also using a select" do
+    assert_equal authors(:david), authors(:david).essays.includes(:writer).first.writer
+
+    assert_nothing_raised do
+      authors(:david).essays.includes(:writer).select(:name).any?
+    end
+  end
+
   test "preloading with a polymorphic association and using the existential predicate" do
     assert_equal authors(:david), authors(:david).essays.includes(:writer).first.writer
 
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 2aa6d643a5..562cfe6796 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -824,6 +824,16 @@ class RelationTest < ActiveRecord::TestCase
     assert_raises(ActiveRecord::ActiveRecordError) { Author.limit(10).delete_all }
   end
 
+  def test_select_with_aggregates
+    posts = Post.select(:title, :body)
+
+    assert_equal 11, posts.count(:all)
+    assert_equal 11, posts.size
+    assert posts.any?
+    assert posts.many?
+    assert_not posts.empty?
+  end
+
   def test_select_takes_a_variable_list_of_args
     david = developers(:david)