I've several times wanted a way to add multiple select output columns using a
single expression. A typical scenario would be if the columns come from a
subselect from another table where repeating the subselect means slow
performance as well as awkward and repetitive code.
Sometimes the subselect can be rewritten as a join, but that is not always the
case. Consider something like:
select customer.*,
(select avg(amount),sum(amount) from purchases
where purchases.customer_id = customer.customer_id
) as (avg_purchase, total_purchase),
(select avg(amount),sum(amount) from quotes
where quotes.customer_id = customer.customer_id
) as (avg_quote, total_quote)
from customer
(Ok, actually that could be done as a join using some trickery with GROUP BY,
but I have other scenarios where it can't because the subselects overlap.)
With the new support for complex data types like arrays and structures perhaps
I could do this by constructing a RECORD in each subselect and then wrapping
another layer around the query where I explicitly list each element of the
RECORD that I want to include in the result set.
But it would be nice to have some more convenient mechanisms for handling this
case.
--
greg
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