Re: primary key and uniqueness

From: "Martin A. Marques" <martin@math.unl.edu.ar> > >On Fri, 23 Jun 2000, you wrote: > > From: "Martin A. Marques" <martin@math.unl.edu.ar> > > > > > >Is it posible to create a table like this > > > > > >CREATE TABLE usuario ( > > > U_id SERIAL PRIMARY KEY UNIQUE, > > > U_nombre NCHAR(50), > > >);> > > > I don't know. Is it? Have you tried it? What happened? > >Got an error! ;-) Perfectly reasonable error too! > > >The question would be if I can combine "PRIMARY KEY" with "UNIQUE". Can >I > > >make any kind of combination of constraints? > > > > In this case PRIMARY KEY includes UNIQUE, so why would you want to? In >fact, > > this produces error 577 "this type of constraint already exists on this > > column set". So, technically, the answer to your question is no. > >So with PRIMARY KEY I get it all! Do I get some other constraint? In what way? >One last one. Is it posible to reference a field on a table to a field on >another table that is not a PRIMARY KEY? No. Not using declarative syntax, anyway. ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com