> At 06:27 AM 28/08/2005 +0000, you wrote:
> >Please see below answer...
> >
> >AFAIK you can have as many UINQUEs on a table as you want. But anyway:
> >You
> >can make sure by using a before InsertUpdate-trigger checking for an
> >exists(select FIELD from table where FIELD=VALUE) on your FIELD and
> >VALUE.
> >..............................
> >
> >....My question..
> >How to define UNIQUE on a column>?
>
> You need a UNIQUE constraint on a column or group of columns to make it
> available as a REFERENCES target for a foreign key constraint. A unique
> index is created for the UNIQUE constraint, but an index that is defined
> with the UNIQUE attribute is *not* a UNIQUE constraint.

a ha! and that's why the user table in security.fdb has a unique index and
not a constraint or a primary key
Alan

>
> e.g.
>
> >Also..what is VALUE above, a variable declared in trigger..?
>
> In a trigger, VALUE would be the "NEW." context variable for the
> column in
> the trigger's owning table that is being checked. There is a "NEW."
> context variable available for every column in a table in an INSERT or
> UPDATE trigger. There is also a similar set of "OLD." variables
> available
> to UPDATE and DELETE triggers.
>
> ...
> IF (exists(select FIELD from table where FIELD=NEW.ThisColumn)) then
>
> ./heLen