oracle中用start with...connect by prior子句实现递归查询[例子不错]
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今天在做权限这一块,碰到要读取oracle中的树形结构,所以就用到了start with...connect by prior。所以留个脚印以后碰到可以看看。
在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:
//如果只用connect by 而不加 prior 查找的将是 level 为1的一级。
select ... from tablename start with cond1
connect by prior cond2
where cond3;
这里的where是不能加的,我一加一个where就报 sql命令未正确结束的错误。如果有人可以加上去使用,那也请高手我下吧。本人先谢谢了。
不过可以先写 where 然后使用 connect by prior 例如:select * from Sysfunction where nodetype='4' start with parentid ='123'(值) connect by prior functionid=parentid order by level(关键字:级别),parentid, funorder;
简单说来是将一个树状结构存储在一张表里,比如一个表中存在两个字段:
id,parentid那么通过表示每一条记录的parent是谁,就可以形成一个树状结构。
用上述语法的查询可以取得这棵树的所有记录。
其中cond1 是根结点的限定语句,当然可以放宽限定条件,以取得多个根结点,实际就是多棵树。
cond2是连接条件,其中用prior表示上一条记录,比如 connect by prior id=parentid就是说上一条记录的ID是本条记录的parentid,即本记录的父亲是上一条记录。
cond3是过滤条件,用于对返回的所有记录进行过滤。
对于oracle进行简单树查询(递归查询)
deptid paredeptid name
number number char (40 Byte)
部门id 父部门id(所属部门id) 部门名称
通过子节点向根节点追朔.
复习一下:start with ...connect by 的用法, start with 后面所跟的就是就是递归的种子。
递归的种子也就是递归开始的地方 connect by 后面的"prior" 如果缺省:则只能查询到符合条件的起始行,并不进行递归查询;
connect by prior 后面所放的字段是有关系的,它指明了查询的方向。
下面看下几个例子:
create table automobiles(
part_id number(5)
constraint pk_auto_part_id primary key,
parent_id number(5)
constraint fk_auto_ppid_ references automobiles(part_id),
part_cname varchar2(30) not null,
part_ename varchar2(30) not null,
mp_cost number(9,2),
desribe varchar2(20)
);
--插入数据
insert into automobiles values( 1,null,'汽车','mobile',84321.99,'Assembly');
insert into automobiles values( 2,1,'车身','bodywork',19892.99,'Manufacture');
insert into automobiles values( 3,1,'发送机','engine',42128,'Purchase');
insert into automobiles values( 4,1,'附件','attached',15212,'Assembly');
insert into automobiles values( 5,2,'保险杠','bumper',4812.95,'Purchase');
insert into automobiles values( 6,2,'底盘','chassis',12795.11,'Manufacture');
insert into automobiles values( 7,2,'行李箱','Boot',812.11,'Manufacture');
--分层sql脚本语句练习
select level,part_id,parent_id,part_cname,part_ename,mp_cost,desribe
from automobiles
start with part_id=1
connect by prior part_id=parent_id
order by level;
--缩进显示
select level,
lpad(' ',2*level-1)||part_cname||' '||part_ename as partName
from automobiles
start with part_id=1
connect by prior part_id=parent_id
order by level;
--使用子查询 当然也可以在from中加入条件来达到子查询的效果
select level,lpad(' ',2*level-1)||part_cname||' '||part_ename as partName from automobiles
start with part_id=(select part_id from automobiles where part_cname like '%轴%')
connect by prior part_id=parent_id
order by level;
--自底向上的遍历
select level,lpad(' ',2*level-1)||part_cname||' '||part_ename as partName
from automobiles
start with part_id=(select part_id from automobiles where part_cname like '%轴%')
connect by prior parent_id=part_id
order by level;
--删除指定的节点
select level,lpad(' ',2*level-1)||part_cname||' '||part_ename as partName from automobiles
where part_cname <> '底盘'
start with part_id=1
connect by prior parent_id=part_id
order by level;
--删除分支
select level,lpad(' ',2*level-1)||part_cname||' '||part_ename as partName from automobiles
start with part_id=1
connect by prior parent_id=part_id and part_cname <> '底盘'
order by level;
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