1、创建测试表，
create table test_tbl_a(num number);
create table test_tbl_b(num number);
2、插入测试数据；
insert into test_tbl_a values (1);
insert into test_tbl_a values (2);
insert into test_tbl_b values (1);
insert into test_tbl_b values (2);
insert into test_tbl_