Need help using count over function

Question

I have the following query
Select student_id, OM, TM, TP, count(rownum) over (order by OM desc) PS from
(select
er.student_id, sum(er.obtained_marks) OM, sum(ds.max_marks) TM,
to_char(sum(er.obtained_marks)/sum(ds.max_marks)*100,'990.00') TP
from
tbl_exam_results er, tbl_date_sheet ds
where
ds.date_sheet_id = er.date_sheet_id and ds.class_id = 77 and ds.exam_id = 3 and ds.session_id = 1 group by er.student_id
results in
<div style="width: 889px"><div class="fielddata"><div>
<div>STUDENT_ID OM TM TP PS
1825 291 300 97.00 1
3717 290 300 96.67 2
2122 289 300 96.33 3
3396 287 300 95.67{color:#ff6600} *5 &lt;--*{color}
4554 287 300 95.67{color:#ff6600} *5 &lt;--*{color}
1847 281 300 93.67 6
1789 279 300 93.00 7
5254 277 300 92.33 8
1836 258 300 86.00 9
4867 250 260 96.15 10
1786 249 300 83.00 11
4659 245 300 81.67 12
1835 241 300 80.33 *{color:#ff6600}15 &lt;--{color}*
1172 241 270 89.26*{color:#ff6600} 15 &lt;--{color}*
3696 241 300 80.33 *{color:#ff6600}15 &lt;--{color}*
3865 234 300 78.00 16
5912 215 300 71.67 17
5913 204 300 68.00 *{color:#ff6600}19 &lt;--{color}*
3591 204 300 68.00 *{color:#ff6600}19 &lt;--{color}*
1830 184 250 73.60 20
</div>
</div>
</div>
</div>
<div style="width: 889px"><div class="fielddata"><div>
But I want as following
<div>STUDENT_ID OM TM TP PS
1825 291 300 97.00 1
3717 290 300 96.67 2
2122 289 300 96.33 3
3396 287 300 95.67 *{color:#ff6600}4 &lt;={color}*
4554 287 300 95.67 *{color:#ff6600}4 &lt;={color}*
1847 281 300 93.67 {color:#ff6600}5 the following entry{color}
1789 279 300 93.00 6
5254 277 300 92.33 7
1836 258 300 86.00 8
4867 250 260 96.15 9
1786 249 300 83.00 10
4659 245 300 81.67 11
1835 241 300 80.33 {color:#ff6600}*12 &lt;=*{color}
1172 241 270 89.26{color:#ff6600} *12 &lt;=*{color}
3696 241 300 80.33 {color:#ff6600}*12 &lt;=*{color}
3865 234 300 78.00{color:#ff6600} 13 the following entry{color}
5912 215 300 71.67 14
5913 204 300 68.00 *{color:#ff6600}15&lt;={color}*
3591 204 300 68.00 *{color:#ff6600}15 &lt;={color}*
1830 184 250 73.60 {color:#ff6600}16{color} {color:#ff6600}the following entry{color}
</div>
Thanks in advance for any help
</div>
</div>
</div>
<div style="width: 889px"></div>
Edited by: sabir786 on Jan 14, 2009 4:13 AM
Edited by: sabir786 on Jan 14, 2009 4:17 AM

Answer 1

Since I do not understand at all what you are trying to do, I cannot correct your query, but I can explain the results.
The analytic function is doing a running count of the number of records that have been outout so far. With no duplicates, this is somewhat clearer.
SQL> WITH t AS (SELECT 1 om FROM dual UNION ALL
  2             SELECT 2 FROM dual UNION ALL
  3             SELECT 3 FROM dual UNION ALL
  4             SELECT 4 FROM dual UNION ALL
  5             SELECT 5 FROM dual)
  6  SELECT om, COUNT(rownum) OVER (ORDER BY om) ps
  7  FROM t;
        OM         PS
         1          1
         2          2
         3          3
         4          4
         5          5However, when you have duplicates, both duplicate values get the running count from the last of the duplicates (i.e. the highest running count). Here, I have duplicated 4 and see what I get:
SQL> WITH t AS (SELECT 1 om FROM dual UNION ALL
  2             SELECT 2 FROM dual UNION ALL
  3             SELECT 3 FROM dual UNION ALL
  4             SELECT 4 FROM dual UNION ALL
  5             SELECT 4 FROM dual UNION ALL
  6             SELECT 5 FROM dual)
  7  SELECT om, COUNT(rownum) OVER (ORDER BY om) ps
  8  FROM t;
        OM         PS
         1          1
         2          2
         3          3
         4          5
         4          5
         5          6The "second" 4 record had a running count of 5 (i.e. it was the fifth record output), so both 4's get the same count. Changing the order by to descending shows the same effect, it just changes the running count:
SQL> WITH t AS (SELECT 1 om FROM dual UNION ALL
  2             SELECT 2 FROM dual UNION ALL
  3             SELECT 3 FROM dual UNION ALL
  4             SELECT 4 FROM dual UNION ALL
  5             SELECT 4 FROM dual UNION ALL
  6             SELECT 5 FROM dual)
  7  SELECT om, COUNT(rownum) OVER (ORDER BY om DESC) ps
  8  FROM t;
        OM         PS
         5          1
         4          3
         4          3
         3          4
         2          5
         1          6John