Oracle “CONNECT BY” 用法

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

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

[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

DEPID DEPNAME                                                                           UPPERDEPID

----------- -------------------------------------------------------------------------------- -----------

0 General Deparment                                                                

1 Development                                                                                0

2 QA                                                                                         0

3 Server Development                                                                         1

4 Client Development                                                                         1

5 TA                                                                                         2

6 Porject QA                                                                                 2

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

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

例2：

1.根据树形结构查子类

select * from xxxx where levelpermission = 0 and validflag = 1

start with id = '20130718091552GRP60000001'

connect by prior id=PARENTID

2. 根据属性结构查询父类

select * from xxxx where levelpermission = 0 and validflag = 1

start with id = '40288181455dbe1701455ee92b9d001d'

connect by prior PARENTID=id

例三：

通过CONNECT BY生成序列

SQL> SELECT ROWNUM FROM DUAL CONNECT BY ROWNUM <= 5;

ROWNUM

----------

1

2

3

4

5

http://www.cnblogs.com/lettoo/archive/2010/08/03/1791239.html