connect by和strart with子句

--使用connect by和strart with子句
SELECT [level],column,expression, ...
FROM table
[WHERE where_clause]
[[START WITH start_condition] [CONNECT BY prior_condition]];

SELECT  empno,
           mgr,
           ename,
           job
      FROM emp
START WITH mgr IS NULL
CONNECT BY PRIOR empno = mgr;

 
--使用偽列level
SELECT LEVEL,
           empno,
           mgr,
           ename,
           job
      FROM emp
START WITH mgr IS NULL
CONNECT BY PRIOR empno = mgr
  ORDER BY LEVEL, mgr, empno;
 

--格式化層次查詢的結果
SELECT LEVEL,
           empno,
           mgr,
          lpad(' ',2*level-1)||ename as employee,
           job
      FROM emp
START WITH mgr is null
CONNECT BY PRIOR empno = mgr;

--從非根節點開始遍歷
SELECT LEVEL,
           empno,
           mgr,
           lpad(' ',2*level-1)||ename as employee,
           job
      FROM emp
START WITH ename like 'JONES'
CONNECT BY PRIOR empno = mgr;

--在start with子句中使用子查詢
  SELECT LEVEL,
           empno,
           mgr,
           lpad(' ',2*level-1)||ename as employee,
           job
      FROM emp
START WITH empno=(select empno from emp where ename='CLARK')
CONNECT BY PRIOR empno = mgr;

--向上遍歷
SELECT LEVEL,
           empno,
           mgr,
           lpad(' ',2*level-1)||ename as employee,
           job
      FROM emp
START WITH ename like 'JONES'
CONNECT BY PRIOR mgr=empno;

--從層次化查詢中刪除節點
SELECT LEVEL,
           empno,
           mgr,
           lpad(' ',2*level-1)||ename as employee,
           job
      FROM emp
WHERE ename !='JONES'
START WITH mgr is null
CONNECT BY PRIOR empno = mgr;

--上面的查詢雖然刪除了節點但是並沒有刪除該節點的分支，為了連同分支也一併刪除，在connect by子句中使用and子句
SELECT LEVEL,
           empno,
           mgr,
           lpad(' ',2*level-1)||ename as employee,
           job
      FROM emp
START WITH mgr is null
CONNECT BY PRIOR empno = mgr
AND  ename !='JONES';

--在層次化查詢中加入其它條件
SELECT LEVEL,
           empno,
           mgr,
           lpad(' ',2*level-1)||ename as employee,
           job,
           sal
      FROM emp
WHERE sal<3000     
START WITH mgr is null
CONNECT BY PRIOR empno = mgr;