Re: "Subquery must return only one column" & query optimization

"Philippe Lang" <philippe.lang@attiksystem.ch> writes:
> I was trying to run this query this morning:

> --------------------------
> SELECT 

> r.*,

> (
>     SELECT 

>     rl.reminder_header,
>     rl.reminder_footer

>     FROM reminder_levels AS rl
>     WHERE rl.lookup =
>     (
>         SELECT MAX(reminder_level_lookup) 
>         FROM reminders
>         WHERE customer_id = r.customer_id
>     )
> )

> FROM reminders AS r
> --------------------------

> Postgresql replied that:

> --------------------------
> ERROR: subquery must return only one column

Since 8.0 or so you could write the sub-select as
SELECT ROW(rl.reminder_header, rl.reminder_footer) FROM ...

We ought to make that happen automatically, but it's not real
high on the to-do list.
        regards, tom lane