postgresql 第一列null排在前，然后再按第二列的顺序排序

表

# select * from jinbo.persons;
 id | lastname | firstname |    address    |   city   
----+----------+-----------+---------------+----------
  3 | Snow     | Jon       | Oxford Street | London
  1 | Adams    | Jonn      | Oxford Street | London
  2 | Bush     | George    | Fifth Avenue  | New York
  4 | Rose     | Leslie    |               | 
  5 | Rose     | Alice     |               | 
(5 rows)

排序要求

比如展示要把address为null的放在最前边，其他排序依赖address 地址出现的次数排序,sql 如下：

# select address, count(1) from jinbo.persons group by address order by ( case when address is null then 1 else 0 end ) desc;
    address    | count 
---------------+-------
               |     2
 Fifth Avenue  |     1
 Oxford Street |     2