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  • oracle中connect by prior的使用

    作用

    connect by主要用于父子,祖孙,上下级等层级关系的查询

    语法

    { CONNECT BY [ NOCYCLE ] condition [AND condition]... [ START WITH condition ]
    | START WITH condition CONNECT BY [ NOCYCLE ] condition [AND condition]...}

    解释:

    start with: 指定起始节点的条件

    connect by: 指定父子行的条件关系

    prior: 查询父行的限定符,格式: prior column1 = column2 or column1 = prior column2 and ... ,

    nocycle: 若数据表中存在循环行,那么不添加此关键字会报错,添加关键字后,便不会报错,但循环的两行只会显示其中的第一条

    循环行: 该行只有一个子行,而且子行又是该行的祖先行

    connect_by_iscycle: 前置条件:在使用了nocycle之后才能使用此关键字,用于表示是否是循环行,0表示否,1 表示是

    connect_by_isleaf: 是否是叶子节点,0表示否,1 表示是

    level: level伪列,表示层级,值越小层级越高,level=1为层级最高节点

    例子

    自定义数据

     1 -- 创建表
     2 create table employee(
     3        emp_id number(18),
     4        lead_id number(18),
     5        emp_name varchar2(200),
     6        salary number(10,2),
     7        dept_no varchar2(8)
     8 );
     9 
    10 -- 添加数据
    11 insert into employee values('1',0,'king','1000000.00','001');
    12 insert into employee values('2',1,'jack','50500.00','002');
    13 insert into employee values('3',1,'arise','60000.00','003');
    14 insert into employee values('4',2,'scott','30000.00','002');
    15 insert into employee values('5',2,'tiger','25000.00','002');
    16 insert into employee values('6',3,'wudde','23000.00','003');
    17 insert into employee values('7',3,'joker','21000.00','003');commit;

     查询以emp_id为0开始的节点的所有直属节点

     1 select emp_id,lead_id,emp_name,prior emp_name as lead_name,salary
     2 from employee
     3 start with  lead_id=0
     4 connect by prior emp_id =  lead_id 
     5 
     6 -- 等同于
     7 select emp_id,lead_id,emp_name,prior emp_name as lead_name,salary
     8 from employee
     9 start with  emp_id=1
    10 connect by prior emp_id =  lead_id

      查询以emp_id为6开始的节点

    1 select emp_id,lead_id,emp_name,salary
    2 from employee 
    3 start with emp_id=6
    4 connect by prior lead_id=emp_id;

     level伪列的使用,格式化层级

    1 select lpad(' ',level*2,' ')||emp_name as name,emp_id,lead_id,salary,level
    2 from employee
    3 start with lead_id=0
    4 connect by prior emp_id=lead_id

     connect_by_root 查找根节点

    1 select connect_by_root emp_name,emp_name,lead_id,salary
    2 from employee  
    3 where dept_no='002'
    4 start with lead_id=1
    5 connect by  prior emp_id = lead_id;

     标注循环行

    1 -- 插入一条数据,与另一条emp_id=7的数据组成循环行
    2 insert into employee 
    3 values('3',7,'joker_cycle','21000.00','003');
    4 commit;
    5 -- connect_by_iscycle("CYCLE"), connect by nocycle
    6 select emp_id,emp_name,lead_id,salary,connect_by_iscycle as cycle 
    7 from employee 
    8 start with lead_id=0
    9 connect by nocycle prior emp_id = lead_id;

     connect_by_isleaf 是否是叶子节点

    1 select emp_id,emp_name,lead_id,salary,connect_by_isleaf
    2 from employee
    3 start with lead_id=0
    4 connect by nocycle prior emp_id=lead_id;

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  • 原文地址:https://www.cnblogs.com/lgx5/p/12799900.html
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