Re: [SQL] Tricky SQL (?)

Use a temporary table.

Peter Eisentraut wrote:
> 
> Let's say I have a table of credits with a customer number attached to it
> and a table of refunds with a customer number attached to it. Occasionally
> I want to go through this list and check if any customers still have
> more credits summed up than refunds.
> 
> The technically correct choice for a query would be something like
> 
> SELECT customer_nr, sum(amount) FROM ( SELECT customer_nr, amount FROM
> credits UNION customer_nr, -amount FROM refunds ) GROUP BY customer_nr
> HAVING sum(amount)>0;
> 
> Unfortunately, this doesn't work because subselects are not allowed in the
> target list. The current solution is to read in all credits and refunds
> and have the application (some PHP, some Perl) do the summing and
> filtering. But this doesn't only seem clumsy but it creates unneccessay
> network traffic.
> 
> Seemingly, this should be a common problem, like invoices vs. payments,
> assets vs. liabilities, etc. Does anyone have suggestions on how to tackle
> this? I am open to changes in the table structure, too.
> 
> --
> Peter Eisentraut
> PathWay Computing, Inc.

-- 
Chris Bitmead
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