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Oracle start with..Connect By prior..用法实例讲解

2014-05-21 10:26 573 查看


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:


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