update arc_ceshiyong2 set item_no=isnull(item_no,0)+1
where recid='2019072315075604892075992428'

​​https://zhidao.baidu.com/question/577975320.html?qbl=relate_question_3&word=sql%20null%2B1​​

update tableName set num=isnull(num,0) + isnull(接收到的数,0) where id=​​XXX​​