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首先创建
一张表menu记录菜单的层级情况。
表结构如下：
menu_id number,
parent_id number,
menu_name nvarchar2(20)
插入数据：
insert into MENU (MENU_ID, PARENT_ID, MENU_NAME)
values (1, null, 'AAAA');
insert into MENU (MENU_ID, PARENT_ID, MENU_NAME)
values (2, 1, 'BBBB');
insert into MENU (MENU_ID, PARENT_ID, MENU_NAME)
values (3, 1, 'CCCC');
insert into MENU (MENU_ID, PARENT_ID, MENU_NAME)
values (4, 1, 'DDDD');
insert into MENU (MENU_ID, PARENT_ID, MENU_NAME)
values (5, 2, 'EEEE');
insert into MENU (MENU_ID, PARENT_ID, MENU_NAME)
values (6, 2, 'FFFF');
insert into MENU (MENU_ID, PARENT_ID, MENU_NAME)
values (7, 2, 'GGGG');
insert into MENU (MENU_ID, PARENT_ID, MENU_NAME)
values (8, 3, 'HHHH');
commit;
查询语句：
select rpad(' ',(level-1)*3)||menu_name from menu
connect by parent_id = prior menu_id
start with parent_id is null
connect by 子句定义表中的各个黄是如何相互联系的
start with 子句定义数据黄查询的初始起点
level 表示查询深度
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