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