sql查询存在一张表而不存在另外一张表的三种方法

1. select distinct A.ID from  A where A.ID not in (select ID from B);

2. select A.ID from A left join B on A.ID=B.ID where B.ID is null;

3. select * from  B where (select count(1) as num from A where A.ID = B.ID) = 0