At 02:00 PM 2/2/02 +0100, =?iso-8859-2?Q?Moravecz_L=E1szl=F3?= wrote:

>
>If IB know this select:
> select city, country, (select currency from country B where A.country =
>B.country) from customer A;
>
>why don't know it:
> select city, country, (select currency, country from country B where
>A.country = B.country) from customer A;
>

A legitimate architectural question, I believe.

The short answer is that that is the way SQL works. The select
expression returns a single, scalar value, not a table. For
the select expression to be meaningful in a boolean expression,
it must have these semantics. A select expression used in a
select list could, I suppose, be extended to return multiple
rows and several columns (problematic), but it would have
different semantics than a select expression used elsewhere,
enough to drive any implementor nuts.

Jim Starkey