I need to generate unique and consecutive numbers (for use on an invoice), in a fast and reliable way. currently use a Oracle sequence, but in some cases generated numbers are not consecutive because of exceptions that may occur.

I thought a couple of solutions to manage this problem, but neither of they convincing me. What solution do you recommend?

1. Use a select max ()

   SELECT MAX (NVL (doc_num, 0)) +1 FROM invoices
   

2. Use a table to store the last number generated for the invoice.

   UPDATE docs_numbers
       SET last_invoice = last_invoice + 1
   

3. Another Solution?