MERGE vs REPLACE

It seems to me that it has always been implicitly assumed around here 
that the MERGE command would be a substitute for a MySQL-like REPLACE 
functionality.  After rereading the spec it seems that this is not the 
case.  MERGE always operates on two different tables, which REPLACE 
doesn't do.

That said, what kind of support for insert-or-update-this-row do we want 
to provide, if any?  Should it be a REPLACE command, an extension of 
the INSERT command, a modication of the MERGE syntax, or something 
else?

-- 
Peter Eisentraut
http://developer.postgresql.org/~petere/