Pivot Query with Top N

Question

Oracle 10g
I have formed the following query;
select cell
     , plot_number
     , max(decode(drnk, '1', tree_height*100)) ht_1
     , max(decode(drnk, '2', tree_height*100)) ht_2
     , max(decode(drnk, '3', tree_height*100)) ht_3
  from (select cell
             , plot_number
             , tree_height
             , drnk
          from (select cell
                     , plot_number
                     , tree_height
                     , dense_rank() over (partition by plot_number order by tree_height desc)drnk
                  from jip_recovery
         where drnk <= 3
           and tree_height is not null
         order by tree_height desc
group by cell, plot_number
order by cell, plot_numberThis query is supposed to take data like this and pivot it for the three tallest trees;
select cell, plot_number, tree_height from jip_recovery where cell = 'C01' and plot_number = 10151;
CELL PLOT_NUMBER            TREE_HEIGHT           
C01  10151                  14.01                 
C01  10151                  21.33                 
C01  10151                  16.06                 
C01  10151                  16.88                 
C01  10151                  18.29                 
C01  10151                  12.27                 
6 rows selected When I include a filter for CELL and PLOT NUMBER like this;
select cell
     , plot_number
     , max(decode(drnk, '1', tree_height*100)) ht_1
     , max(decode(drnk, '2', tree_height*100)) ht_2
     , max(decode(drnk, '3', tree_height*100)) ht_3
  from (select cell
             , plot_number
             , tree_height
             , drnk
          from (select cell
                     , plot_number
                     , tree_height
                     , dense_rank() over (partition by plot_number order by tree_height desc)drnk
                  from jip_recovery
                 where cell in ('C01')
                   and plot_number in (10151)
         where drnk <= 3
           and tree_height is not null
         order by tree_height desc)
group by cell, plot_number
order by cell, plot_numberIt returns the correct values in the three columns
CELL PLOT_NUMBER            HT_1                   HT_2                   HT_3                  
C01  10151                  2133                   1829                   1688                   But when I remove the filter to run it on the complete dataset some 546000 records it returns nulls for some of the HT_% columns. Of special interest in this example is the record for plot number 10151 and 10153.;
CELL PLOT_NUMBER            HT_1                   HT_2                   HT_3                  
C01  8198                   2652                   2105                   2075                  
C01  8199                   2338                   2107                   2012                  
C01  10151                                         2133                                         
C01  10153                                         1993                   1628                  
C01  10154                  2151                   2135                   1976
...Can anyone see what I am doing wrong?
Ben

Answer 1

Yes, you missed cell from the partition.