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丸趣 TV 小编给大家分享一下 Oracle 如何实现层次化查询,相信大部分人都还不怎么了解,因此分享这篇文章给大家参考一下,希望大家阅读完这篇文章后大有收获,下面让我们一起去了解一下吧!
Oracle 层次化查询
(1) 树状模型
假如有一个市场模型,其中一级市场是中国,二级市场是省份,三级市场是各个省下面的市,四级市场是各个市下面的县。那么可以创建表 market:
create
table market(market_id number(2), market_name varchar2(10),
parent_market_id number(2));
insert
all
into
market values(1, China , 0)
into
market values(2, Shan Xi , 1)
into
market values(3, Shan Dong , 1)
into
market values(4, Fu Jian , 1)
into
market values(5, Tai Yuan , 2)
into
market values(6, Yang Quan , 2)
into
market values(7, Qi Zhou , 2)
into
market values(8, Qing Dao , 3)
into
market values(9, Ji Nan , 3)
into
market values(10, Yan Tai , 3)
into
market values(11, Xia Men , 4)
into
market values(12, Fu Zhou , 4)
into
market values(13, Quan Zhou , 4)
into
market values(14, Gu Jiao , 5)
into
market values(15, Yang Qu , 5)
into
market values(16, Qing Xu , 5)
select
* from dual;
(2) 层次化查询
select
market_id, market_name
from
market
start
with market_name = Shan Xi
connect
by prior market_id = parent_market_id;
MARKET_ID
MARKET_NAME
———-
——————————
2 Shan Xi
5 Tai Yuan
14
Gu Jiao
15
Yang Qu
16
Qing Xu
6 Yang Quan
7 Qi Zhou
7
rows selected.
这里的搜索规则为:从 Shan
Xi 节点开始搜索、前一个节点的 market_id 等于下一个节点的 parent_markket_id。
(3) 相关函数
显示搜索路径的函数为
sys_connect_by_path(列名,分隔符)
示例:
select
market_id, market_name, sys_connect_by_path(market_name, /) as
market_path
from
market
start
with market_name = Gu Jiao
connect
by prior parent_market_id = market_id;
MARKET_ID
MARKET_NAM MARKET_PATH
———-
———- —————————————-
14
Gu Jiao /Gu Jiao
5 Tai Yuan /Gu Jiao/Tai Yuan
2 Shan Xi /Gu Jiao/Tai Yuan/Shan Xi
1 China /Gu Jiao/Tai Yuan/Shan Xi/China
这里可以利用 max() 函数来获得完整的路径:
select
max(sys_connect_by_path(market_name, /)) market_path
from
market
start
with market_name = Gu Jiao
connect
by prior parent_market_id = market_id;
MARKET_PATH
—————————————-
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