Felix,
> Is is it possible to write an aggregation function which returns
> more than one row?
Yes - if I have understood your requirement correctly.
It would have been helpful if you had given some idea of the
application/what you want to achieve. Here's an example from out of my
imagination: if there is a table holding details of all of the sales
(invoiced lines) for a particular month's trading, and if each is
recorded/credited against a particular salesperson. Let's say there are one
million rows in the table, but only ten sales staff. You can ask MySQL to
return the sum of (aggregate) all sales attributed to each salesperson, and
to count the number of sales/lines for each person:
SELECT SalespersonNm-or-ID,
COUNT( * ) AS NumberOfSales,
SUM( ExtendedValue) AS TValueOfSales
FROM =tbl=
WHERE =this-month=
GROUP BY SalespersonNm
This will analyse the million rows but only output ten lines of
results/salespersons' names (and the NumberOfSales column's entries will add
up to one million/the number of rows in the table).
What you wanted?
=dn
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