how to constrain a query to return 1 or 0 rows (or >1 or 0 rows)

[Kevin Murphy]

This is probably a stupid question, but ...

I'd like to be able to take an existing query and modify it to return a
single row if that's what the base query returns, and 0 rows if the
base query returns multiple rows. Similarly, I'd like to also modify
it to return multiple rows if that's what the base query returns, and 0
rows if the base query return a single row.

What's a good way to do this?

Thanks,
Kevin Murphy
---------------------------(end of broadcast)---------------------------
TIP 8: explain analyze is your friend

[Bruno Wolff III]

On Fri, Sep 10, 2004 at 17:39:31 -0400,
Kevin Murphy <mu****@genome.chop.edu> wrote:

This is probably a stupid question, but ...

I'd like to be able to take an existing query and modify it to return a
single row if that's what the base query returns, and 0 rows if the
base query returns multiple rows. Similarly, I'd like to also modify
it to return multiple rows if that's what the base query returns, and 0
rows if the base query return a single row.

What's a good way to do this?

SELECT * FROM whatever HAVING count(*) < 1;

---------------------------(end of broadcast)---------------------------
TIP 3: if posting/reading through Usenet, please send an appropriate
subscribe-nomail command to ma*******@postgresql.org so that your
message can get through to the mailing list cleanly