创建一个demo表 department：
create table department (
code VARCHAR2(10) not null,
name VARCHAR2(50),
pcode VARCHAR2(10),
mgrname VARCHAR2(50)
);
insert into department values('ROOT','顶级部门', null, 'R大大');
insert into department values('A','A部门', 'ROOT', 'A老大');
insert into department values('A01','A01部门', 'A', 'A01老大');
insert into department values('A02','A02部门', 'A', 'A02老大');
insert into department values('B','B部门', 'ROOT', 'B老大');
insert into department values('B01','B01部门', 'B', 'B01老大');
insert into department values('B02','B02部门', 'B', 'B02老大');
1.递归查询某个部门的所有子级部门：
select t.* from department t start with t.code='ROOT' connect by prior t.code = t.pcode ;
查询结果：
2.递归查询某个部门的所有上级部门：
select t.* from department t start with t.code='B02' connect by t.code = prior t.pcode ;
查询结果：
