一个查询的奇怪问题

select id from follow where mid=‘1000’ 查询无结果
下面这句却能查出一条结果，我就想不通怎么跑出来的
select name from staff where id in (select id from follow where mid='1000')

但如果改成select name,id from staff where id in (select id from follow where mid='1000') 就正常了 没结果

select id from follow where mid=‘1000’
这货是全角的单引号！