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Connect By

程序员文章站 2022-06-26 08:24:45
connect by 用于存在父子,祖孙,上下级等层级关系的数据表进行层级查询。 语法格式: { CONNECT BY [ NOCYCLE ] condition [AND condition]... [ START WITH condition ] | START WITH condition C ......

connect by 用于存在父子,祖孙,上下级等层级关系的数据表进行层级查询。

 

语法格式:
    { connect by [ nocycle ] condition [and condition]... [ start with condition ]
    | start with condition connect by [ nocycle ] condition [and condition]...
    }

 

特殊词讲解

    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

-- 创建表
create table employee(
       emp_id number(18),
       lead_id number(18),
       emp_name varchar2(200),
       salary number(10,2),
       dept_no varchar2(8)
);

-- 添加数据
insert into employee values('1',0,'king','1000000.00','001');
insert into employee values('2',1,'jack','50500.00','002');
insert into employee values('3',1,'arise','60000.00','003');
insert into employee values('4',2,'scott','30000.00','002');
insert into employee values('5',2,'tiger','25000.00','002');
insert into employee values('6',3,'wudde','23000.00','003');
insert into employee values('7',3,'joker','21000.00','003');
commit;

 Connect By

 

(1) 查询以lead_id为0开始的节点的所有直属节点

 select emp_id,lead_id,emp_name,prior emp_name as lead_name,salary
 from employee
 start with  lead_id=0
 connect by prior emp_id =  lead_id 

 -- 等同于

select emp_id,lead_id,emp_name,prior emp_name as lead_name,salary
from employee
start with  emp_id=1
connect by prior emp_id =  lead_id 

Connect By

 

 

(2) 以emp_id为6的所有祖先节点

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

 Connect By

 

 

(3) 查询一个节点的叔叔伯父节点

       with t as (
       select  employee.*,prior emp_name,level le
       from employee 
       start with lead_id = 0
       connect by lead_id=prior emp_id
       )
       select *
       from t 
       left join t tt on tt.emp_id=6
       where t.le = (tt.le-1)
       and t.emp_id not in (tt.lead_id)   

 Connect By

 

 

(4) 查询族兄

       with t as (
            select employee.*,prior emp_name,level le
           from employee 
           start with lead_id=0
           connect by lead_id= prior emp_id
       )
       select t.*
       from t  t
       left join t tt on tt.emp_id=6
       where t.le=tt.le and t.emp_id<>6;

Connect By

 

 

(5) level伪列的使用,格式化层级

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

Connect By

level数值越低级别越高

 

 

(6) connect_by_root 查找根节点

select connect_by_root emp_name,emp_name,lead_id,salary
from employe 
start with lead_id=1
connect by prior emp_id = lead_id;

 Connect By

 

 

(7) 标注循环行

-- 插入一条数据,与另一条emp_id=7的数据组成循环行
insert into employee values('3',7,'joker_cycle','21000.00','003');
commit;

 

-- connect_by_iscycle("cycle"), connect by nocycle
select emp_id,emp_name,lead_id,salary,connect_by_iscycle as cycle 
from employee 
start with lead_id=0
connect by nocycle prior emp_id = lead_id;

 Connect By

最后一行与新追加的一行是循环关系,因此connect_by_iscycle列显示值为1,但结果集只显示循环的第一条,与之循环的另外一条(新追加的一条)是不显示的

connect by 后面的nocycle关键字是防止出现父子关系循环的,如果表中出现父子关系循环且没有使用该关键字,会报如下错误:

--ora-01436: 用户数据中的 connect by 循环

 

 

(8) connect_by_isleaf 是否是叶子节点

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

Connect By

叶节点指的是没有子节点的节点,那些是既是父节点又是子节点的节点不属于叶节点