我使用了以下sql，它的工作正常，但是我也需要排序空字符串。请给我指导。
@H_404_4@SELECT id,first_name,last_name FROM users ORDER BY first_name DESC NULLS LAST limit 10;
SELECT id,first_name,last_name FROM users ORDER BY first_name DESC NULLS LAST limit 10;
ORDER BY NULLIF(first_name,'') DESC NULLS LAST
