Re: exclusion constraint for ranges of IP

On 23/08/2011, at 13:31, Jasen Betts wrote:

> On 2011-08-23, Herouth Maoz <herouth@unicell.co.il> wrote:
>
>>    EXCLUDE USING GIST  ( customer_id WITH =, is_default WITH AND )
>
>
>> Basically, each customer can have several rows in this table, but only =
>> one per customer is allowed to have is_default =3D true. Is this exclude =
>> constraint correct?
>
> I don't really understand exclude, but instead of EXCLUDE... I would do
>
> CREATE UNIQUE INDEX "invoice_definitions-unique-default"
>  ON invoice_definitions(customer_id) WHERE is_default;
>
> Which would create a smaller (and probably faster) BTREE index
> containing only the rows with is_default true.

This is an interesting concept.  It's a different angle on the same condition.

>
> There seems to be no way to create this in the create-table
> command. (using 8.4 here)

Yes, it's curious that exclude constraints are the only ones which are allowed to be partial in a table definition.

Thank you.

Herouth