Hierarchy using loop

Question

Hi,
Can someone explain me how to find the level using loop/cursor not using connect by clause.
It is just for playing.
Thank you

Answer 1

Hi,
If you needed to write your own function, here's one way you could do it:
CREATE OR REPLACE FUNCTION     emp_level
(       in_empno       IN      scott.emp.empno%TYPE
RETURN     PLS_INTEGER
IS
--          emp_level returns the hierarchy level of the employee with in_emp_id
--          If that employee has no mgr, then it returns 1.
--          If that employee has a manager, then it finds the given employee's mgr,
--              that employee's mgr, and so on until it reaches the top of the tree,
--              and returns the total number of meployees in the chain.
     return_level     PLS_INTEGER           := 0;     -- To be returned
     this_empno     scott.emp.empno%TYPE  := in_empno;
BEGIN
     WHILE  this_empno  IS NOT NULL
     LOOP
--          dbms_output.put_line (this_empno || ' = this_empno');     -- For debugging only
          SELECT  mgr
          INTO     this_empno
          FROM     scott.emp
          WHERE     empno     = this_empno;
          return_level := return_level + 1;
     END LOOP;
     RETURN     return_level;
EXCEPTION
     WHEN NO_DATA_FOUND
     THEN
          RETURN  NULL;     -- Bogus in_empno or corrupt table
END  emp_level;
/You could also use a recursive function.
Notice the commented-out call to dbms_output.put line inside the loop. Whenever you write a loop, you might want to include a call to print like this. If you get into an infinite loop, it will soon cause a buffer overflow, and you won't have to kill the session. Remember to delete the line, or comment it out, when you're sure the loop works correctly.
In pure SQL, this would be hard to do, because there is no real recursion in SQL parat from CONNECT BY (or, starting in Oracle 11, a recursive WITH clause, as Pollywog mentioned above).
MODEL can do iteration, but it can be tricky getting it to do the right number of levels. You might have to guess high, for example, assume that there will never be more than 100 levels. You might be able to do something with the number of rows actulayy in the table. For example, the scott.emp table has 14 rows, so you know you will never have a chain of command the goes more than 14 levels. (The actual maximum depth happens to be 4.)
using dynamic SQL, you could do a self-join, with a different copy of the table for each possible level. This is not very efficient, and hard to code.
I assume your table uses the Adjacency Model , like scott.emp, where every node has pointer to its parent.
There are other methods of storing trees in a relational database; some of them have fairly straghtfoward ways of finding the level of any given node. It alwyas helps to post a little sample data (CREATE TABLE and INSERT statements).
T.PD wrote:
There is no level pseudo column without connect by .Actually, in Oracle 11, you can use LEVEL in any query. However, if there's no CONNECT BY clause, LEVEL will always be 0.