[dragonwriter]

> Avoid state at all costs. Stored procedures are stateful.

Stored procedures are no more state than application code is.

> Write me a constraint and key arrangement which is unique across two and three columns in separate groups.

What does "unique across two and three columns in separate groups" mean? I get that its something more complex than a simple multicolumn uniqueness constraint, but not what it is supposed to do.

I suspect that whatever it is can be done with PostgreSQL -- possibly using the (relatively) new exclusion constraints -- but I can't quite be sure without more clarity on what you mean.