Tree structure and hierarchical query in oracle Table

1. Here, take the emp table as an example. There is a subordinate-superior relationship between the empno field and the mgr field in this table.

2 look up the top boss from top to bottom, where the level is one of the three pseudo columns

Select level,empno,ename,mgr from emp

Start with empno=7839-subordinate field

Connect by prior empno=mgr;-- subordinate field = superior field

3 check from bottom to top

Select level,empno,ename,mgr from emp

Start with empno=7369-subordinate field

Connect by prior mgr=empno;-- parent field = subordinate field

4-- just filter a single node. Everything under that node is preserved.

Select level,empno,ename,mgr from emp

Where empno7698-subordinate field

Start with empno=7839

Connect by prior empno=mgr;-- subordinate field = superior field

5-filter the entire branch

Select level,empno,ename,mgr from emp

Start with empno=7839-subordinate field

Connect by prior empno=mgr and empno7698;-- subordinate field = superior field