sqlserver中where判断是否执行in

Question

我现在有这样的问题，declare @ id，select * user where id in (@id),当id为空或者为“”时不执行in，
搜索全部，应该怎么写这个语句，求解答，感谢！！

Answer 1

declare @ id，select * user where id in (@id) and not exist (select 1 from user where id is null or id='')