Re: Set generating functions and subqueries

Hi, Tom,

Tom Lane wrote:

> The behavior of the subquery expression is dictated by the SQL spec:
>
> 1) If the cardinality of a <scalar subquery> or a <row subquery> is
> greater than 1, then an exception condition is raised: cardinal-
> ity violation.

That's interesting to know, and it seems to be a clean design.

> The fact that the other form is even allowed is more of a holdover from
> PostQUEL than something we have consciously decided is a good idea.
> (IMHO it's actually a fairly *bad* idea, because it does not work nicely
> when there's more than one SRF in the same targetlist.) It'll probably
> get phased out someday, if we can find a way to replace the
> functionality. I seem to recall speculating that SQL2003's LATERAL
> tables might do the job.

AFAICS, it can be replaced with JOINs:

select * FROM (SELECT 'othercol' AS other) as foo CROSS JOIN (SELECT
generate_series(1,2) as a) as fop CROSS JOIN (SELECT
generate_series(3,4) as b) AS foq;
other | a | b
----------+---+---
othercol | 1 | 3
othercol | 2 | 3
othercol | 1 | 4
othercol | 2 | 4
(4 rows)

> No kidding.

I wasn't kidding, I just wanted to point out the different behaviour
between equal-length and inequal-length sequences.

Thanks,
markus

--
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf. | Software Development GIS

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