Oracle “CONNECT BY” 使用

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

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

0 General
Deparment

1
Development
0

2
QA
0

3 Server
Development
1

4 Client
Development
1

5
TA
2

6 Porject
QA
2

7 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

[例2]

通过CONNECT BY生成序列

SQL> SELECT ROWNUM FROM DUAL CONNECT BY ROWNUM
<= 10;

ROWNUM

----------

1

2

3

4

5

6

7

8

9

10

10 rows selected

[例3]

通过CONNECT BY用于十六进度转换为十进制

CREATE OR REPLACE FUNCTION f_hex_to_dec(p_str IN
VARCHAR2) RETURN VARCHAR2 IS

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

-- 对象名称:
f_hex_to_dec

-- 对象描述:
十六进制转换十进制

-- 输入参数:
p_str 十六进制字符串

-- 返回结果:
十进制字符串

-- 测试用例:
SELECT f_hex_to_dec('78A') FROM dual;

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

v_return VARCHAR2(4000);

BEGIN

SELECT
SUM(DATA) INTO v_return

FROM (SELECT (CASE upper(substr(p_str, rownum, 1))

WHEN 'A' THEN '10'

WHEN 'B' THEN '11'

WHEN 'C' THEN '12'

WHEN 'D' THEN '13'

WHEN 'E' THEN '14'

WHEN 'F' THEN '15'

ELSE substr(p_str, rownum, 1)

END) * power(16, length(p_str) - rownum) DATA

FROM dual

CONNECT BY rownum <= length(p_str));

RETURN
v_return;

EXCEPTION

WHEN OTHERS
THEN

RETURN NULL;

END;

说明：

1. CONNECT BY rownum <=
length(p_str))对输入的字符串进行逐个遍历

2. 通过CASE语句，来解析十六进制中的A-F对应的10进制值

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