--oracle中的树状结构查询实际上就是一个中序遍历
--显示以KING为根节点的树，start with定义起始节点
SELECT *
FROM emp a
START WITH a.empno = 7839
CONNECT BY PRIOR a.empno = a.mgr;
--置于等号前面，由父节点向子节点方向检索；置于等号后面，则从子节点向父节点方向检索
SELECT *
FROM emp a
START WITH a.empno = 7839
CONNECT BY PRIOR a.empno = a.mgr;
--使用伪列level来显示层级关系
SELECT *
FROM emp a
START WITH a.empno = 7839
CONNECT BY PRIOR a.empno = a.mgr;
SELECT level, a.*
FROM emp a
START WITH a.empno = 7839
CONNECT BY PRIOR a.empno = a.mgr;
--使用函数 sys_connect_by_path 显示全路径
SELECT LEVEL, sys_connect_by_path(a.ename, '/'), a.*
FROM emp a
START WITH a.empno = 7839
CONNECT BY PRIOR a.empno = a.mgr;
--where子句只限定单个节点，不影响子其子节点或者父节点
SELECT LEVEL, sys_connect_by_path(a.ename, '/'), a.*
FROM emp a
WHERE a.empno <> 7369
START WITH a.empno = 7839
CONNECT BY PRIOR a.empno = a.mgr;
--connect by 子句限定整个以当前节点为起始节点的整个分支
--connect_by_root 可以在列之前显示最高节点的内容
SELECT LEVEL, connect_by_root(a.job),sys_connect_by_path(a.ename, '/'), a.*
FROM emp a
WHERE a.empno <> 7369
START WITH a.empno = 7839
CONNECT BY PRIOR a.empno = a.mgr;
--connect_by_isleaf 显示当前行是否叶子节点，1：是；0：否
SELECT LEVEL, connect_by_isleaf,sys_connect_by_path(a.ename, '/'), a.*
FROM emp a
WHERE a.empno <> 7369
START WITH a.empno = 7839
CONNECT BY PRIOR a.empno = a.mgr;
--connect_by_iscycle 10g中开始有的新特性，用来判断当前节点是否产生了循环，0：否；1：是
SELECT LEVEL, connect_by_iscycle, connect_by_isleaf,sys_connect_by_path(a.ename, '/'), a.*
FROM emp a
WHERE a.empno <> 7369
START WITH a.empno = 7839
CONNECT BY NOCYCLE PRIOR a.empno = a.mgr;
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/28313368/viewspace-754072/ ，如需转载，请注明出处，否则将追究法律责任。
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