Oracle start with...connect by prior用法（备忘）

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>;

说明：
<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

 

 

还是看个例子吧，应该能更好的说明问题。数据库表结构如下：

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

  description varchar(10)
);

插入测试数据：

 

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');

 

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--------------------------------------准备好了，开始吧-----------------------------------------

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

 

1. 获取完整树：

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

 

      结构图：

                 |---------a------a1

                 |            |

                 |            |

                 |            |------a2

                 |

                 |---------b------b1

                 |            |

                 |            |

                 |            |------b2

 

2. 获取特定子树：

 2.1 select * from t2 start with id = 1 connect by prior id = root_id;

 

       结构图：

                 |---------a------a1

                 |            |

                 |            |

                 |            |------a2

 

 

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

 

       结构图：

                 |---------b------b1

                 |            |

                 |            |

                 |            |------b2

 

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

例如：

 

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

 

                 |---------a                 

                 |           

                 |

                 |---------b

 

 

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

 

                 |---------a   

 

 

以上内容从其他网友那里copy加工而成，特别感谢实例的原创者！！！