Oracle Connect By Prior用法(实现递归查询)
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Oracle ConnectBy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;
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