#ORACLE 每日一点#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 WITHcondition ]CONNECT BY [ NOCYCLE ] condition The start with .. connect by clause can be used to select data that has a hierarchical relationship (

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 WITHcondition ]
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)notnull,
  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 rowsselected 

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     LEVELPATH
------------------------------ ------------------- ---------- ---------- --------------------------------------------------------------------------------
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 rowsselected 

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> SELEC TROWNUM FROM DUAL CONNECT BY ROWNUM 
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_strINVARCHAR2)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 (CASEupper(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 

说明：
1. CONNECT BY rownum 

2. 通过CASE语句，来解析十六进制中的A-F对应的10进制值