Inserting a Sequence of Numbers

Question

Hi all
I have a number field restricted to 3 digits, and when someone navigates to the block to insert a record I want the number field to display 001 to state this is the first record, then if a second record is inserted put in 002 etc. Currently you can go and put any old 3 digit number in but I want to restrict it to a display field only, showing the number of records in this block in a sequence, for a particular parent record.
I am trying to work out the following:
How to build a counting generator (the most obvious bit)
How to get the count generator to recognise what the existing number is (related to the parent record) and insert the next sequence of number say it is 001, then it now needs to put in 002.
I currently have this piece of code (and result) as a start and am finding it difficult to decide how to build on it from that:
SELECT ltrim (to_char (rownum, '009'))
FROM dual
LTRI
001
Any ideas on this would be appreciated.
Thanks
USER605593

Answer 1

If you had a date column which held the date the row was added (or whatever it is that denotes the order) then you don't need to bother with an explicit sub sequence in the table.
eg.
with my_data as (select 1 record_id, 'hello' val, trunc(sysdate) -1 date_inserted from dual union all
                 select 1 record_id, 'there' val, trunc(sysdate) -1 + 2/24 date_inserted from dual union all
                 select 1 record_id, 'sailor' val, trunc(sysdate) -1 + 5/24 date_inserted from dual union all
                 select 1 record_id, 'boy' val, trunc(sysdate) -1 + 18/24 date_inserted from dual union all
                 select 2 record_id, 'hi' val, trunc(sysdate) -1 + 1/24 date_inserted from dual union all
                 select 2 record_id, 'ho' val, trunc(sysdate) -1 + 12/24 date_inserted from dual union all
                 select 2 record_id, 'off to work' val, trunc(sysdate) -1 + 13/24  date_inserted from dual union all
                 select 2 record_id, 'we go' val, trunc(sysdate) -1 + 23/24  date_inserted from dual union all
                 select 3 record_id, 'good' val, trunc(sysdate) -1 + 1.5/24 date_inserted from dual union all
                 select 3 record_id, 'bye' val, trunc(sysdate) -1 + 5/24 date_inserted from dual union all
                 select 4 record_id, 'geronimo' val, trunc(sysdate) -1 + 4/24 date_inserted from dual)
-- end of data setup. Query below:
select record_id, val, row_number() over (partition by record_id order by date_inserted) rn
from   my_data
RECORD_ID     VAL     RN
1     hello     1
1     there     2
1     sailor     3
1     boy     4
2     hi     1
2     ho     2
2     off to work     3
2     we go     4
3     good     1
3     bye     2
4     geronimo     1This has the added advantage that if you need to insert a row at the end or in the middle, the ordering will automatically be taken care of. If you store the number, you then have to work out a way of updating the sub-sequence number manually. (Obviously, you'll have to format the rn into the 3 digit format for your display purposes, but you already know how to do that.)