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SYS_CONNECT_BY_PATH函式用法 ORACLE

SELECT ename   
FROM scott.emp    
START WITH ename = 'KING'    
CONNECT BY PRIOR empno = mgr;    
  
--得到結果為:   
  
KING   
JONES   
SCOTT   
ADAMS   
FORD   
SMITH   
BLAKE   
ALLEN   
WARD   
MARTIN   
TURNER   
JAMES   
  
  
  
而:   
  
  
  
SELECT SYS_CONNECT_BY_PATH(ename, '>') "Path"    
FROM scott.emp    
START WITH ename = 'KING'    
CONNECT BY PRIOR empno = mgr;   
  
  
  
--得到結果為:   
  
  
  
>KING   
>KING>JONES   
>KING>JONES>SCOTT   
>KING>JONES>SCOTT>ADAMS   
>KING>JONES>FORD   
>KING>JONES>FORD>SMITH   
>KING>BLAKE   
>KING>BLAKE>ALLEN   
>KING>BLAKE>WARD   
>KING>BLAKE>MARTIN   
>KING>BLAKE>TURNER   
>KING>BLAKE>JAMES   
>KING>CLARK   
>KING>CLARK>MILLER  
SELECT ename
FROM scott.emp 
START WITH ename = 'KING' 
CONNECT BY PRIOR empno = mgr;

--得到結果為:

KING
JONES
SCOTT
ADAMS
FORD
SMITH
BLAKE
ALLEN
WARD
MARTIN
TURNER
JAMES

而:

SELECT SYS_CONNECT_BY_PATH(ename, '>') "Path" 
FROM scott.emp 
START WITH ename = 'KING' 
CONNECT BY PRIOR empno = mgr;

--得到結果為:

>KING
>KING>JONES
>KING>JONES>SCOTT
>KING>JONES>SCOTT>ADAMS
>KING>JONES>FORD
>KING>JONES>FORD>SMITH
>KING>BLAKE
>KING>BLAKE>ALLEN
>KING>BLAKE>WARD
>KING>BLAKE>MARTIN
>KING>BLAKE>TURNER
>KING>BLAKE>JAMES
>KING>CLARK
>KING>CLARK>MILLER
 


其實SYS_CONNECT_BY_PATH這個函式是oracle9i才新提出來的!
它一定要和connect by子句合用!
第一個引數是形成樹形式的欄位,第二個引數是父級和其子級分隔顯示用的分隔符!

START WITH 代表你要開始遍歷的的節點!

CONNECT BY PRIOR 是標示父子關係的對應!

如下例子:

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select max(   
substr(   
sys_connect_by_path(column_name,',')   
,2)   
)   
from (select column_name,rownum rn from user_tab_columns where table_name ='AA_TEST')   
start with rn=1 connect by rn=rownum ;  
select max(
substr(
sys_connect_by_path(column_name,',')
,2)
)
from (select column_name,rownum rn from user_tab_columns where table_name ='AA_TEST')
start with rn=1 connect by rn=rownum ;

是將列用,進行分割成為一行,然後將首個,去掉,只取取最大的那個資料。

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

下面是別人的例子:

1、帶層次關係

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SQL> create table dept(deptno number,deptname varchar2(20),mgrno number);   
  
Table created.   
  
SQL> insert into dept values(1,'總公司',null);   
  
1 row created.   
  
SQL> insert into dept values(2,'浙江分公司',1);   
  
1 row created.   
  
SQL> insert into dept values(3,'杭州分公司',2);   
  
1 row created.   
  
SQL> commit;   
  
Commit complete.   
  
SQL> select max(substr(sys_connect_by_path(deptname,','),2)) from dept connect by prior deptno=mgrno;   
  
MAX(SUBSTR(SYS_CONNECT_BY_PATH(DEPTNAME,','),2))   
--------------------------------------------------------------------------------   
總公司,浙江分公司,杭州分公司  
SQL> create table dept(deptno number,deptname varchar2(20),mgrno number);

Table created.

SQL> insert into dept values(1,'總公司',null);

1 row created.

SQL> insert into dept values(2,'浙江分公司',1);

1 row created.

SQL> insert into dept values(3,'杭州分公司',2);

1 row created.

SQL> commit;

Commit complete.

SQL> select max(substr(sys_connect_by_path(deptname,','),2)) from dept connect by prior deptno=mgrno;

MAX(SUBSTR(SYS_CONNECT_BY_PATH(DEPTNAME,','),2))
--------------------------------------------------------------------------------
總公司,浙江分公司,杭州分公司

2、行列轉換


如把一個表的所有列連成一行,用逗號分隔:

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SQL> select max(substr(sys_connect_by_path(column_name,','),2))   
from (select column_name,rownum rn from user_tab_columns where table_name ='DEPT')   
start with rn=1 connect by rn=rownum ;   
  
MAX(SUBSTR(SYS_CONNECT_BY_PATH(COLUMN_NAME,','),2))   
--------------------------------------------------------------------------------   
DEPTNO,DEPTNAME,MGRNO