Oracle 层次查询（Connect By）

-引用别人的表结构

create table test_connect_by (child number,parent number);

insert into TEST_CONNECT_BY (CHILD, PARENT)
values (2, 5);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (3, 5);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (10, 15);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (5, 15);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (9, 17);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (8, 17);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (15, 38);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (17, 38);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (6, 38);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (13, 26);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (1, 26);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (12, 26);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (11, 18);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (7, 18);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (38, null);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (26, null);
insert into TEST_CONNECT_BY (CHILD, PARENT)
values (18, null);
commit;

---------------------------------------

select a.child,
       a.parent,
       level "层次",
       sys_connect_by_path(child, '->') "合并层次",
       prior a.child "父节点",
       connect_by_root a.child "根节点",
       decode(connect_by_isleaf, 1, a.child, null) "子节点",
       decode(connect_by_isleaf, 1, '是', '否') "是否子节点"
from test_connect_by a
start with a.parent is null --从parent为空开始扫描
connect by prior a.child = a.parent --以child为父列连接parent
order siblings by child desc --对层次排序
;

 

 

转贴：

http://blog.chinaunix.net/u1/54706/showart_1711812.html

Oracle Connect By用法

oracle中的select语句可以用START WITH...CONNECT BY PRIOR子句实现递归查询，connect by 是结构化查询中用到的，其基本语法是：

select ... from <TableName> 
where <Conditional-1>
start with <Conditional-2>
connect by <Conditional-3>
;

<Conditional-1>：过滤条件，用于对返回的所有记录进行过滤。
<Conditional-2>：查询结果重起始根结点的限定条件。
<Conditional-3>：连接条件

数据组织结构如下图：

数据库表结构如下：

create table t2(
root_id number,
id number,
name varchar(5),
description varchar(10)
);

insert into t2(root_id,id,name,description) values(0,1,'a','aaa');
insert into t2(root_id,id,name,description) values(1,2,'a1','aaa1');
insert into t2(root_id,id,name,description) values(1,3,'a2','aaa2');
insert into t2(root_id,id,name,description) values(0,4,'b','bbb');
insert into t2(root_id,id,name,description) values(4,5,'b1','bbb1');
insert into t2(root_id,id,name,description) values(4,6,'b2','bbb2');

获取完整树：
select * from t2 start with root_id = 0 connect by prior id = root_id;

获取特定子树：
select * from t2 start with id = 1 connect by prior id = root_id;

select * from t2 start with id = 4 connect by prior id = root_id;

如果connect by prior中的prior被省略，则查询将不进行深层递归。
如：

select * from t2 start with root_id = 0 connect by id = root_id;

select * from t2 start with id = 1 connect by id = root_id;
如：

今天在ITPUB看到的题目

2、有如下信息：
起始地 目的地 距离（公里）
A   B   1000
A   C   1100
A   D   900
A   E   400
B   D   300
D   F   600
E   A   400
F   G   1000
C   B   600
请用SQL语句或一段代码写出从A出发，可达到的目的地（包括间接方式）。

创建表test

SQL> select * from test;

START_PLACE END_PLACE    DISTANCE
----------- ---------- ----------
A           B                1000
A           C                1100
A           D                 900
A           E                 400
B           D                 300
D           F                 600
E           A                 400
F           G                1000
C           B                 600

select start_place, end_place
from (select * from testwhere end_place <> 'A')
start with start_place = 'A'
connect by prior end_place = start_place;

START_PLACE END_PLACE
----------- ----------
A           C
C           B
B           D
D           F
F           G
A           D
D           F
F           G
A           E

这些条目中的END_PLACE就是所有可以从A到达的点

connect by prior 实现树状查询 connect by prior 左边的为父接点，右边为自接点。

oracle还提供函数sys_connect_by_path（）可以把路径表示出来如下面语句

select sys_connect_by_path(start_place, '->')||'->'||end_place
from (select * from duanjw where end_place <> 'A')
start with start_place = 'A'
CONNECT BY PRIOR end_place = start_place;

SYS_CONNECT_BY_PATH(START_PLAC
--------------------------------------------------------------------------------
->A->C
->A->C->B
->A->C->B->D
->A->C->B->D->F
->A->C->B->D->F->G
->A->D
->A->D->F
->A->D->F->G
->A->E

这样看起来就清楚了很多

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/xiaoduan9678/archive/2007/07/05/1680261.aspx