select a.*
   from a
where not exists(select 1
   from b
    where a.id=b.id)

------解决方案--------------------
SQL code


select a.*
   from a
   where a.id not in  (select id
                            from b)

------解决方案--------------------
select * from a where a.id not in(select b.id from b);

------解决方案--------------------
select a.* from a
where not exists (select 1 from b where a.id=b.id);

select a.* from a where a.id not in(select b.id from b);

兩個都行，如果B表中資料較多，用exists.