MAX(SummaryNum) +1 bad idea, but how to use sequence part composite column

Question

Hi,
My relational mode is as follows
Policy (policynum PK) has 1:M with Summary (policynum FK, SummaryNum part of PK, other columns part of PK)
Basically for each policy users can enter notes with SummaryNum 1, 2, 3, 4.... These numbers are shown to the user for tracking purpose. I need to make sure summary notes for EACH policy start with 1 (cannot really use sequence in the table in the strictest sense) and are incremented by 1. The current Oracle form basically creates the next highest possible value of SummaryNum by adding one to the currently available highest value. In brief, it is like a sequence number for summaries of a particular policy in the summary table.
PRE-INSERT
SELECT MAX(SummaryNum ) + 1
FROM Summary
I am trying to replicate this in ADF BC (using 11g) and know that not using sequencing and adding one to get the next number is a very bad idea due to concurrency challenges (transactional ACID properties). The reasons are as follows.
•     Using MAX(policy_memo_seq_num) + 1 is not scalable,
•     It will lead to duplicates in a multi-user environment, whether ADF BC, Oracle Forms, or any other technology
I also know how to use create a sequence in db, a related trigger, and then set the attribute in EO properties as DBSequence. My challenge is that since SummaryNum is not a primary key, and instead is part of a composite key in my case, how do I make sure that summary notes for EACH policy start with 1 in the Summary Table.
I appears that i cannot really use sequence in the table in the strictest sense as this will mean that for policies the summaryNum will start from the next available sequence number, but what i really want is to have it start by one for all policies.*
I would appreciate any help.
Thanks,

Answer 1

Not sure if there is a better way, but here is one way. Let's say your table was like this:
    SQL> desc versioned_item
     Name         Null?    Type
     ID           NOT NULL NUMBER
     VERSION      NOT NULL NUMBER
     DESCRIPTION           VARCHAR2(20)and lets say your data looked like this:
    SQL> select * from versioned_item order by id, version
            ID    VERSION DESCRIPTION
          1001          1 Item 1001
          1001          2 Item 1001
          1001          3 Item 1001
          1002          1 Item 1002
          1002          2 Item 1002
          1003          1 Item 1003To select only the rows for the max-version-id, you could do this:
    select id, version,description
    from versioned_item
    where (id,version) in (select id,max(version) from versioned_item group by id)
    order by id
            ID    VERSION DESCRIPTION
          1001          3 Item 1001
          1002          2 Item 1002
          1003          1 Item 1003To capture this as a view object, you'd only just need to paste in the WHERE clause above into the Where clause box of the view object. No need to use expert-mode since you're not changing the select list or from clause.