The reason why, probably, is that the signed type is an SQL standard,
and unsigned is not. I've noticed that postgres tries to adhere to the
standard and not do too many extensions, particularly in comparison to
MySQL.
MySQL has some nice extensions, but you have to really change things to
go to another database if you've started on MySQL, (as you are
noticing). That has other drawback. What if you are really successful
with a design and company, and your site gets big and you get money to
make it bigger? You decide to go with DB2 or Oracle then, perhaps? You'd
probably have to make all the same changes to your design to port to
those databases, since MySQL is less standardized than all of them.
Postgres seems to be trying to be the open source, standards compliant
DB.
One thing I don't remember seeing in MySQL that might be an extension
you could use in Postgres is INT8. That's a HUGE number, maybe more than
the number of atoms in existence! (probably not, but it's big). It comes
out to 1.844674407371 * 10^19. (That's over a billion, squared). If
you used that, and forced it unsigned with a check, you'd probably have
LOTS more room than you'd need in that value range.
--
Carpe Dancem ;-)
-----------------------------------------------------------------
Remember your friends while they are alive
-----------------------------------------------------------------
Sincerely, Dennis Gearon