Oracle “CONNECT BY” 使用

Oraclesand

2014-06-26

Oracle “CONNECT BY”是层次查询子句，一般用于树状或者层次结果集的查询。其语法是：

[ START WITH condition ]

CONNECT BY [ NOCYCLE ] condition

The start with .. connect by clause can be used to select data that has a hierarchical relationship (usually some sort of parent->child (boss->employee or thing->parts).

说明：

1. START WITH：告诉系统以哪个节点作为根结点开始查找并构造结果集，该节点即为返回记录中的最高节点。

2. 当分层查询中存在上下层互为父子节点的情况时，会返回ORA-01436错误。此时，需要在connect by后面加上NOCYCLE关键字。同时，可用connect_by_iscycle伪列定位出存在互为父子循环的具体节点。 connect_by_iscycle必须要跟关键字NOCYCLE结合起来使用

接下来，用一些示例来说明“CONNECT BY”的用法。

[例1]

创建一个部门表，这个表有三个字段，分别对应部门ID，部门名称，以及上级部门ID

-- Create table
create table DEP
(
DEPID number(10) not null,
DEPNAME varchar2(256),
UPPERDEPID number(10)
)
;

初始化一些数据

SQL> INSERT INTO DEP(DEPID, DEPNAME, UPPERDEPID) VALUES (0, '总经办', null);
1 row inserted
 
SQL> INSERT INTO DEP(DEPID, DEPNAME, UPPERDEPID) VALUES (1, '开发部', 0);
1 row inserted
 
SQL> INSERT INTO DEP(DEPID, DEPNAME, UPPERDEPID) VALUES (2, '测试部', 0);
1 row inserted
 
SQL> INSERT INTO DEP(DEPID, DEPNAME, UPPERDEPID) VALUES (3, 'Sever开发部', 1);
1 row inserted
 
SQL> INSERT INTO DEP(DEPID, DEPNAME, UPPERDEPID) VALUES (4, 'Client开发部', 1);
1 row inserted
 
SQL> INSERT INTO DEP(DEPID, DEPNAME, UPPERDEPID) VALUES (5, 'TA测试部', 2);
1 row inserted
 
SQL> INSERT INTO DEP(DEPID, DEPNAME, UPPERDEPID) VALUES (6, '项目测试部', 2);
1 row inserted
 
SQL> commit;
commit complete

SQL> SELECT * FROM DEP;
 
DEPID DEPNAME UPPERDEPID
----------- -------------------------------------------------------------------------------- -----------
General Deparment 
Development 0
QA 0
Server Development 1
Client Development 1
TA 2
Porject QA 2
 
rows selected

现在我要根据“CONNECT BY”来实现树状查询结果

SQL> SELECT RPAD( ' ', 2*(LEVEL-1), '-' ) || DEPNAME "DEPNAME",
CONNECT_BY_ROOT DEPNAME "ROOT",
CONNECT_BY_ISLEAF "ISLEAF",
LEVEL ,
SYS_CONNECT_BY_PATH(DEPNAME, '/') "PATH"
FROM DEP
START WITH UPPERDEPID IS null
CONNECT BY PRIOR DEPID = UPPERDEPID;
 
DEPNAME ROOT ISLEAF LEVEL PATH
------------------------------ ------------------- ---------- ---------- --------------------------------------------------------------------------------
General Deparment General Deparment 0 1 /General Deparment
-Development General Deparment 0 2 /General Deparment/Development
---Server Development General Deparment 1 3 /General Deparment/Development/Server Development
---Client Development General Deparment 1 3 /General Deparment/Development/Client Development
-QA General Deparment 0 2 /General Deparment/QA
---TA General Deparment 1 3 /General Deparment/QA/TA
---Porject QA General Deparment 1 3 /General Deparment/QA/Porject QA
 
7 rows selected

说明：
1. CONNECT_BY_ROOT 返回当前节点的最顶端节点
2. CONNECT_BY_ISLEAF 判断是否为叶子节点，如果这个节点下面有子节点，则不为叶子节点
3. LEVEL 伪列表示节点深度
4. SYS_CONNECT_BY_PATH函数显示详细路径，并用“/”分隔

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Oracle “CONNECT BY” 使用

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