NTILE Function

Question

After knowing usage of NTILE analytical function, i started using it to divide my rows into batches. However I'd like to pass the expression dynamically (depending on the row count), but unfortunately I see some limitations inhibit me from achieving it. The reason I want to do this dynamically is when there are rows <= expression value, NTILE function forms one batch per each record which I don't wish to happen.
If you observe in the below example, it creates 10 batches/buckets when there are only 10 rows, where I wish to have only 1 batch.
SQL> drop table r_dummy;
Table dropped.
SQL>
SQL> create table r_dummy
  2  as
  3  select level id
  4  from dual
  5  connect by level<=10;
Table created.
SQL>
SQL> select ntile(10) over(order by id) batch_no,id
  2  from r_dummy;
  BATCH_NO         ID
         1          1
         2          2
         3          3
         4          4
         5          5
         6          6
         7          7
         8          8
         9          9
        10         10
10 rows selected.
SQL>
SQL> select ceil(count(*)/10) from r_dummy;
CEIL(COUNT(*)/10)
                1
SQL>I wish to use above same ceil function in my actual query but
with t as
select id, ceil((count(*) over())/10) bucket_size
from r_dummy
select id,ntile(bucket_size) over(order by id) batch_no
from t;
ERROR at line 6:
ORA-30488: argument should be a function of expressions in PARTITION BYI had seen the same question being asked by Sven Weller [url https://forums.oracle.com/forums/thread.jspa?threadID=587782]here, would like to know if there is any workaround available to this.
Please help me.

Answer 1

Hi,
not sure it that fits your need, but I came to this:select batch_no
, least(ntile(&&DOP.) over (order by batch_no), 1+floor(row_number() over (order by batch_no)/(&&MBPG.+1))) grpid
from t;You'd use 2 parameters :
- DOP (Degree of parallelism) = the max number of group to assign batch_unit
- MBPG (Min BatchUnit Per Group) = the min number of batch_unit in a group.
Ok, if only 10 batch unit in total :Scott@my11g SQL>define DOP=4
Scott@my11g SQL>define MBPG=10
Scott@my11g SQL>/
  BATCH_NO      GRPID
         1          1
         2          1
         3          1
         4          1
         5          1
         6          1
         7          1
         8          1
         9          1
        10          1
10 rows selected.Now if 43 batch units :Scott@my11g SQL>/
  BATCH_NO      GRPID
         1          1
         2          1
         3          1
         4          1
         5          1
         6          1
         7          1
         8          1
         9          1
        10          1
        11          1
        12          2
        13          2
        14          2
        15          2
        16          2
        17          2
        18          2
        19          2
        20          2
        21          2
        22          2
        23          3
        24          3
        25          3
        26          3
        27          3
        28          3
        29          3
        30          3
        31          3
        32          3
        33          3
        34          4
        35          4
        36          4
        37          4
        38          4
        39          4
        40          4
        41          4
        42          4
        43          4
43 rows selected.Just adjust DOP and MBPG as you like.