oracle中connect by prior的使用

做用

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，并且子行又是该行的祖先行

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

connect_by_isleaf: 是不是叶子节点，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

-- 建立表
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;

查询以emp_id为0开始的节点的全部直属节点

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

查询以emp_id为6开始的节点

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

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_root 查找根节点

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

标注循环行

-- 插入一条数据，与另外一条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_isleaf 是不是叶子节点

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;