Remove unnecessary ORDER BY clause when counting for all columns

Author: gabriel-amaral

activerecord/lib/active_record/relation/calculations.rb

@@ -673,7 +673,11 @@ def build_count_subquery(relation, column_name, distinct)
         subquery_alias = Arel.sql("subquery_for_count", retryable: true)
         select_value = operation_over_aggregate_column(column_alias, "count", false)
 
-        relation.build_subquery(subquery_alias, select_value)
+        if column_name == :all
+          relation.unscope(:order).build_subquery(subquery_alias, select_value)
+        else
+          relation.build_subquery(subquery_alias, select_value)
+        end
       end
   end
 end

activerecord/test/cases/calculations_test.rb

@@ -309,6 +309,12 @@ def test_no_limit_no_offset
     assert_no_match(/OFFSET/, queries.first)
   end
 
+  def test_no_order_by_when_counting_all
+    queries = capture_sql { Account.order(id: :desc).limit(10).count }
+    assert_equal 1, queries.length
+    assert_no_match(/ORDER BY/, queries.first)
+  end
+
   def test_count_on_invalid_columns_raises
     error = assert_raises(ActiveRecord::StatementInvalid) do
       Account.select("credit_limit, firm_name").count