--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;
