Re: B-tree + sorting + unique constraint

On Wed, Dec 29, 2010 at 5:04 PM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> On Wed, 2010-12-29 at 16:39 -0800, bricklen wrote:
>> -- works:
>> create unique index t_uidx on t (x desc nulls last,y desc nulls last, z asc);
>> drop index t_uidx;
>
> ...
>
>> -- creating the unique constraint with sorting fails:
>> alter table t add constraint t_xyz_uc unique (x desc nulls last,y desc
>> nulls last, z asc);
>>
>> ERROR:  syntax error at or near "desc"
>> LINE 1: alter table t add constraint t_uidx unique (x desc nulls las...
>
> A UNIQUE constraint in a table definition only allows simple column
> references. To get more advanced, you need to use the CREATE UNIQUE
> INDEX syntax you showed above.
>
> Regards,
>        Jeff Davis

Ok, thanks for your reply. I think I'll have to reread the docs to get
a better feel for those little nuances.