准备表和测试数据

create table A(
	id varchar2(10),
  name varchar2(20)
);
create table B(
	id varchar2(10),
  age number
);

insert into A values (101,'zs');
insert into A values (102,'ls');
insert into A values (103,'ww');

insert into B values (101,20);
insert into B values (106,30);
insert into B values (104,23);

需求：选出A有，B没有的ID

方式1：遍历B表的所有ID

select id from A where id not in (select id from B)

方式2：左连接

• 左表中没有和右表匹配的，右表的值会以null填充

select A.*,B.* from A left join B on A.id=B.id where b.id is null