fuyou@ORCL> select deptno,ename,row_number() over(partition by deptno order by empno)rn
2 ,count(*)over(partition by deptno) cnt
3 from emp;
DEPTNO ENAME RN CNT
---------- -------------------- ---------- ----------
10 CLARK 1 2
10 KING 2 2
20 SMITH 1 5
20 JONES 2 5
20 SCOTT 3 5
20 ADAMS 4 5
20 FORD 5 5
30 ALLEN 1 6
30 WARD 2 6
30 MARTIN 3 6
30 BLAKE 4 6
30 TURNER 5 6
30 JAMES 6 6
40 MILLER 1 1
fuyou@ORCL> select deptno,sys_connect_by_path(ename,',') as emps
2 from (select deptno,ename,row_number() over(partition by deptno order by empno)rn
3 ,count(*)over(partition by deptno) cnt
4 from emp)
5 where level=cnt
6 connect by prior deptno = deptno and prior rn = rn-1
7 ;
DEPTNO
----------
EMPS
10
,CLARK,KING
20
,SMITH,JONES,SCOTT,ADAMS,FORD
30
,ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES
40
,MILLER
fuyou@ORCL> select deptno,ltrim(sys_connect_by_path(ename,',') ,',')as emps
2 from (select deptno,ename,row_number() over(partition by deptno order by empno)rn
3 ,count(*)over(partition by deptno) cnt
4 from emp)
5 where level=cnt
6 connect by prior deptno = deptno and prior rn = rn-1
7 ;
DEPTNO
----------
EMPS
10
CLARK,KING
20
SMITH,JONES,SCOTT,ADAMS,FORD
30
ALLEN,WARD,MARTIN,BLAKE,TURNER,JAMES
40
MILLER
在此例子中，使用rn來作爲遍歷樹
start with rn=1 --rn=1的爲根 併爲每遇到rn=1，創建一個新的列表
對使用了connect by 的level從1開始
connect by prior deptno = deptno and prior rn = rn-1
//上一行記錄的deptno 等於 下一行的deptno 的deptno 且上一行的rn 等於下一行的rn-1
sys_connect_by_path使用迭代方式構建此列表
sys_connect_by_path 會在列表最前面增加一個所選定的分隔符，每迭代一次會在當前的列加增加分隔符
另一例子：
fuyou@ORCL> select rpad('*',2*level,'*')||ename ename
2 from emp
3 start with mgr is null--mgr 爲空爲根
4 connect by prior empno = mgr;--前一行的empno 等於下一行的mgr 以這樣的方式來構建
ENAME
**KING
****JONES
******SCOTT
********ADAMS
******FORD
********SMITH
****BLAKE
******ALLEN
******WARD
******MARTIN
******TURNER
******JAMES
****CLARK
******MILLER
已選擇14行。
fuyou@ORCL> spool off
下面這個例子容易明白
fuyou@ORCL> select rpad('*',2*level,'*')||ename ename,empno,mgr
2 from emp
3 start with mgr is null
4 connect by prior empno = mgr;
ENAME
EMPNO MGR
---------- ----------
**KING
7839
****JONES
7566 7839
******SCOTT
7788 7566
********ADAMS
7876 7788
******FORD
7902 7566
********SMITH
7369 7902
****BLAKE
7698 7839
******ALLEN
7499 7698
******WARD
7521 7698
******MARTIN
7654 7698
******TURNER
7844 7698
******JAMES
7900 7698
****CLARK
7782 7839
******MILLER
7934 7782
已選擇14行。
fuyou@ORCL> spool off