zoukankan      html  css  js  c++  java
  • Oracle Connect By的用法

    Oracle Connect By用法
    首先他是针对一种有着父子结构的数据模型而产生的一种方案。
    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:

    select rownum

    from dual

    connect by rownum < 100;

  • 相关阅读:
    C#方法Extra
    C#方法
    C#类型与变量
    归并排序算法
    2020 CiGA Game Jam活动总结
    插入排序算法
    游戏开发随笔
    2019厦门大学信息学院人工智能/智能科学与技术系夏令营(非计算机系)
    基于Dlib、OpenCV开发人脸识别程序的开发建议
    CCF CSP 201703
  • 原文地址:https://www.cnblogs.com/xinzhuangzi/p/4100427.html
Copyright © 2011-2022 走看看