Function sometimes return wrong data

Question

Hi all.
I have a very strange problem with a function. Situation is this: I have an application that handles processes. Each process have a number of steps that is arranged in a matrix like layout. User clicks a step to start/execute it.
Now in a list of current processes i want to have an indication of how "far" a process has reached so i created a function for that and included that in my processlist fetch.
gchs_user_process_steps is the table where the user data for the process step is
gchs_process_steps is the definition table of what steps a process has
gchs_steps is the definition table of all steps
The below function is supposed to return latest step user clicked in the display matrix. tier is used to store the column number and sortorder is the row number of any step user clicked.
CREATE OR REPLACE FUNCTION FN_REACHEDSTEP(p_user_process_id NUMBER)
RETURN VARCHAR IS
  ret VARCHAR(30);
  ret_id INTEGER;
  ret_num INTEGER;
BEGIN
   ret := '';
   ret_id := 0;
   ret_num := 0;
   BEGIN
SELECT substr(step_name,1,30),step_id,reached INTO ret,ret_id,ret_num
FROM (
SELECT a.*, rownum rnum
FROM (
    SELECT s.name AS step_name, ps.id AS step_id, max((ps.tier*1000)+ps.sortorder) AS reached
    FROM gchs_user_process_steps ups, gchs_process_steps ps, gchs_steps s
    WHERE ups.gchs_process_step_id=ps.id AND
       ps.gchs_step_id=s.id AND
       ups.gchs_user_process_id=p_user_process_id
    GROUP BY s.name,ps.id
    ORDER BY 3 DESC) a
WHERE rownum <= 1 )
WHERE rnum >= 1;
   EXCEPTION
     WHEN OTHERS THEN
        ret:='';
   END;     
      RETURN ret;
  EXCEPTION
WHEN OTHERS THEN
       ret := '';
   RETURN ret;
END FN_REACHEDSTEP;
Now the problem is that the function sometimes return wrong value. The name of the step that is returned is not the one i get if i run the SQL by itself.
So doing a
SELECT substr(step_name,1,30),step_id,reached INTO ret,ret_id,ret_num
FROM (
SELECT a.*, rownum rnum
FROM (
    SELECT s.name AS step_name, ps.id AS step_id, max((ps.tier*1000)+ps.sortorder) AS reached
    FROM gchs_user_process_steps ups, gchs_process_steps ps, gchs_steps s
    WHERE ups.gchs_process_step_id=ps.id AND
       ps.gchs_step_id=s.id AND
       ups.gchs_user_process_id=21680
    GROUP BY s.name,ps.id
    ORDER BY 3 DESC) a
WHERE rownum <= 1 )
WHERE rnum >= 1;
and a
select fn_ReachedStep(21680) from dual;
will sometimes return different values.
So is the function fundamentally wrong or is there any cache or something that i've missed that could hold "old" function outputs or am i missing something else.
Thankful for any clues.
I'm using Oracle 10.2.0.1.0
Best regards
/Tomas
Edit: Here's some data that the system uses.
gchs_steps
ID           NAME
10000     Step 1
10020     Step 2
10021     Step 3
10022     Step 4
10023     Step 5
10060     Step 6
10140     Step 7
gchs_process_steps
ID          GCHS_STEP_ID      TIER     SORTORDER
10000     10000               0          1
10001     10020               1          1                                                                                                                   
10002     10021               1          2                                                                                                                   
10003     10022               2          1
10020     10023               3          5
10060     10060                3          4
10080     10140               3          2
10040     10040               3          3
10100     10160               4          3
10160     10220               4          2
11640     11640               3          1
11660     11660               0          6
11661     11661               0          7
11600     11600               0          4
11620     11620               4          1
gchs_user_process_steps
ID          GCHS_USER_PROCESS_ID     GCHS_PROCESS_STEP_ID
35541     21680                         10002
38441     21680                         10020
38440     21680                         10000
52062     21680                         10060
Relations beween table is
gchs_user_process_steps.gchs_process_step_id=gchs_process_steps.id
and
gchs_process_steps.gchs_step_id=gchs_steps.id
So doing the SQL alone will always return
SUBSTR(..)     STEP_ID REACHED
Step 5      10020 3005
but executing the function sometimes returns
FN_REACHEDSTEP(21680)
Step 6
Also removing the rownum limits return and doing a
SELECT s.name AS step_name, ps.id AS step_id, max((ps.tier*1000)+ps.sortorder) AS reached
FROM gchs_user_process_steps ups, gchs_process_steps ps, gchs_steps s
WHERE ups.gchs_process_step_id=ps.id AND
ps.gchs_step_id=s.id AND
ups.gchs_user_process_id=21680
GROUP BY s.name,ps.id,ps.tier, ps.sortorder
ORDER BY 3 DESC
give this result
STEP_NAME     STEP_ID     REACHED
Step 5          10020     3005
Step 6          10060     3004
Step 3          10002     1002
Step 1          10000     1
Edited by: user4935832 on 2008-sep-19 01:38

Answer 1

ORDER BY 3 DESC) a
WHERE rownum <= 1 )
WHERE rnum >= 1;Just some thoughts.
1. You could replace "ORDER BY 3" by "ORDER BY reached"
2. the rownum <=1 and rnum>=1 will return only one row... I don't understand the second one.
Lastly, the difference might come from a duplicate value return by your MAX() function.
If there is two rows (or more) with same MAX, Oracle might return one row arbitrary.
To get the same row, you have to use some aggregation function like MAX() KEEP (DENSE_RANK LAST...).
Here a try for your query, obviously not tested :
SELECT max(substr(step_name,1,30)) keep (dense_rank last order by reached) as step_name,
       max(step_id) keep (dense_rank last order by reached,step_name) as step_id,
       max(reached) as reached
FROM   (SELECT s.name AS step_name,
               ps.id AS step_id,
               max((ps.tier*1000)+ps.sortorder) AS reached
        FROM   gchs_user_process_steps ups,
               gchs_process_steps ps,
               gchs_steps s
       WHERE   ups.gchs_process_step_id=ps.id
       AND     ps.gchs_step_id=s.id
       AND     ups.gchs_user_process_id=21680
       GROUP BY s.name,ps.id) a;Nicolas.