Re: Constraint that compares and limits field values

>Michael Fuhr <mike(at)fuhr(dot)org> wrote on 01/25/2006 10:25:38 AM:
> In 8.1, and in earlier versions if you create a cast from boolean
> to integer, you could do this:
>
> ALTER TABLE event
> ADD CONSTRAINT two_nulls_1 CHECK (
> (evenid1 IS NOT NULL)::int +
> (evevid1 IS NOT NULL)::int +
> (evreid1 IS NOT NULL)::int = 1);
>
> This works because the cast converts true to 1 and false to 0;
> you're adding up the number of true expressions and requiring that
> the sum equal 1 (i.e., that exactly one expression be true).
>
> --
> Michael Fuhr

I am in version 7.3 and it will not let me cast, I get message "ERROR:
Cannot cast type boolean to integer". I will save this for when I upgrade.

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