Top n analysis using hierarchial queries

Question

hi all,
can we do top n analysis in hierarchial queries using level pseudo columns. if so please give an example.
thanks and regards,
sri ram.

Answer 1

Hi,
Analytic functions (such as RANK) often interfere with CONNECT BY queries. Do one of them in a sub-query, and the other in a super-query, as shown below.
If you do the CONNECT BY first, use ROWNUM (which is assigned after ORDER SIBLINGS BY is applied) to preserve the order of the CONNECT BY query.
WITH     connect_by_results     AS
     SELECT     LPAD ( ' '
               , 3 * (LEVEL - 1)
               ) || ename          AS iname
     ,     sal
     ,     ROWNUM               AS r_num
     FROM     scott.emp
     START WITH     mgr     IS NULL
     CONNECT BY     mgr     = PRIOR empno
     ORDER SIBLINGS BY     ename
SELECT       iname
,       sal
,       RANK () OVER (ORDER BY sal DESC)     AS sal_rank
FROM       connect_by_results
ORDER BY  r_num
;Output:
INAME                  SAL   SAL_RANK
KING                  5000          1
   BLAKE              2850          5
      ALLEN           1600          7
      JAMES            950         13
      MARTIN          1250         10
      TURNER          1500          8
      WARD            1250         10
   CLARK              2450          6
      MILLER          1300          9
   JONES              2975          4
      FORD            3000          2
         SMITH         800         14
      SCOTT           3000          2
         ADAMS        1100         12 
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only), and the results you want from that data. If you use only commonly available tables (such as those in the scott or hr schemas), then you don't have to post any sample data; just post the results.
Explain how you get those results from that data.
Always say what version of oracle you're using.