Oracle Connect By Prior用法（实现递归查询）

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

例如：

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');

如图：





1.获取完整树：

select * from t2;

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



2.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;





3.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;