Re: interesting sequence

It is simpler, but it will result in id collision if two inserts runs at the same time, particularly if the count query takes a while to run, so be prepared to handle that.  Make sure you have an index which can satisfy that count query quickly.  If you are not using the C locale for your database, that means you must create an index on that column that uses text_pattern_ops or varchar_pattern_ops (depending on if it is text or varchar column) so that postgresql can use the index for that comparison, otherwise LIKE clauses will force a sequential scan of the whole table every time.  C locale does byte by byte text comparison, so the special index isn't required.