Q

Performing hierarchical queries

I have an employee table in Oracle that has 100 records: some employees are managers and under these managers there

will be some clerks, and under some clerks there will be some typists. I need to retreive the heirarchical structure of managers, ie. who is working under whom and who is the manager of whom, like manager--clerk--typist, something like a tree structure in SQL Server. Can you help me please?

Oracle has a nice?albeit non-standard?way to perform hierarchical queries: the CONNECT BY clause. Here's an example using Oracle's sample EMP table:

select lpad(' ',(Level-1)*3) || EName || 
       ' (' || Job || ')' as "Employee Tree"
  from Emp
  connect by prior EmpNo = Mgr
  start with Mgr is null;
 
And here are the resulting rows:
Employee Tree
------------------------
KING (PRESIDENT)
   JONES (MANAGER)
      SCOTT (ANALYST)
         ADAMS (CLERK)
      FORD (ANALYST)
         SMITH (CLERK)
   BLAKE (MANAGER)
      ALLEN (SALESMAN)
      WARD (SALESMAN)
      MARTIN (SALESMAN)
      TURNER (SALESMAN)
      JAMES (CLERK)
   CLARK (MANAGER)
      MILLER (CLERK)

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This was first published in May 2002

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