Trouble with SEQUENCE, loosing numbers

Question

Hi all, I use a sequence to generate the number of an invoice like this:
Insert into table
values(owner.sequence_name.nextval);
But, if an error occurs this number get lost because of the way the sequence works, how can I avoid this??, there is another way to do it??? It doesnt matter if that solution doesn't use the sequence, but my design cannot accept numbers like 1,3,4,5,7, it has to be 1,2,3,4,5,6,7....
Leo
null

Answer 1

Unfortunately, this is another one of those concepts that sounds simple but isn't.
Yours is not an Oracle (or any other DB) problem; it is a design problem.
The reason that none of the suggested alternatives solve your problem is that there are undefined elements in your requirements.
There are actually two aspects to your of problem: 1) generating unique sequential numbers and 2) using those numbers.
I would suggest starting over and try to clearly define the problem and the requirements.
For example your stated requirements appear to be something like:
1. Invoice numbers must to be unique
2. Invoice numbers must be numeric
3. The first invoice number must be 27 (modify per your requirements)
4. Each new invoice must be numbered one higher than the previous invoice.
5. Invoice numbers must be sequential with no missing numbers.
While the above list seems to be complete there are some very important questions that are not yet answered.
1. When does an invoice become an invoice? That is, when is the invoice number assigned? Is the number assigned before or after the invoice record is committed to the database? If the number is assigned before committing (e.g. when the user begins processing an invoice) but the invoice is then abandoned and never committed there will be a gap in invoice numbers.
2. Can invoice records ever be deleted? If a committed record is deleted there will be a gap in the numbers. Some systems handle deletions by either flagging the records as deleted without actually deleting them or moving the records to a deleted table so that all invoice numbers are always accounted for.
Check printing applications used to print on pre-numbered check forms. The line printers that were used had sprockets to feed the checks and the first check could not be printed on since the sprockets were above the print head. The operator would enter the first check number into the system and the application created a check record marked VOID for that check number. This ensured that all pre-printed checks were accounted for and had not been misplaced or stolen.
Oracle's sequence generator can generate sequence numbers in sequential order and ensure that there are no gaps in the generation process.
Oracle cannot ensure that your application uses those numbers in a way that avoids gaps.
Even a normal INSERT trigger that might be used to get the next sequence value cannot be certain that the record it is inserting will actually be committed unless the COMMIT operation is performed within the trigger.
Sorry to 'rain on your parade' but withouth a better problem definition we can't give you a better solution.