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  • Oracle start with.connect by prior子句实现递归查询

     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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  • 原文地址:https://www.cnblogs.com/sand-tiny/p/3635790.html
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