At 07:07 PM 23/11/2003 +0700, you wrote:

>Helen Borrie wrote:
> > 1) the "@" symbol makes absolutely no difference to the uniqueness of your
> > local + host combination.
>
>Yes it does. Try local="ab", host="c" vs. local="a", host="bc". The
>second will be incorrectly rejected by the UNIQUE(local,host) constraint
>but correctly accepted by UNIQUE(local,ampersand,host).

No, you are mistaken. The index does *not* get concatenated: it stays as
two distinct columns. So you will have:

Local Host
ab c (a unique combination)
a bc (another unique combination)

heLen