Gap-less sequence where multiple transactions with multiple tables are involved

Question

I have a requirement (by law) for a gap-less numbers on different tables. The IDs can have holes in them but not the sequences.

This is something I have to either so

Answer 1

Gap-less sequences are hard to come by. I suggest to use a plain serial column instead. Create a view with the window function row_number() to produce a gap-less sequence:

CREATE VIEW foo AS
SELECT *, row_number() OVER (ORDER BY serial_col) AS gapless_id
FROM   tbl;