A B, 24.01.2011 11:16:
> Hello there!
>
> If I want to create a table
>
> create table users (
> id integer
> name varchar(8)
> enabled boolean
> );
>
> and a constraint unique(id,name) but the unique constraint should
> only be used for the enabled users, how can I do that?
>
> The only way I can think of is to use null values when a user is not
> enabled and use the constraint unique(id,name,enable).
>
You can create a unique index:
create unique index idx_users
on users (id, name)
where enabled;
Note there is a slight difference between a unique constraint and an unique index: the index cannot be used for foreign key reference (the unique constraint could). But that's the only difference as far as I know.
Regards
Thomas