SYS_CONNECT_BY_PATH 函数用法 ORACLE

SELECT ename

FROM scott.emp

START
WITH ename = 'KING'

CONNECT BY PRIOR empno = mgr;

--
得到结果为：

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;

--得到结果为：

>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;

--得到结果为：

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;

--得到结果为：

>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

其实SYS_CONNECT_BY_PATH这个函数是oracle9i才新提出来的！

它一定要和connect by子句合用！

第
一个参数是形成树形式的字段，第二个参数是父级和其子级分隔显示用的分隔符！

START WITH 代表你要开始遍历的的节点！

CONNECT BY PRIOR 是标示父子关系的对应！

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 ;

是将列用,进行分割成为一行，然后将首个，去掉，只取取最大的那个数据。

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

下面是别人的例子：

1、带层次关系

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SQL> create table dept(deptno
number,deptname varchar2(20),mgrno number);

Table
created.

SQL> insert into dept values(1,'总公司',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))

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

总公司,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,'总公司',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))

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

总
公司,浙江分公司,杭州分公司

2、行列转换

如把一个表的所有列连成一行，用逗号分隔:

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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