On Thu, 2002-01-24 at 13:00, Markus Bertheau wrote: Hello again, here's another question: suppose there's a
tablepersonen: personen_id int primary key, data text and a table orders: order_id int primary key,
personen_idint, data text
Might as well do it the "Postgres Way".
CREATE TABLE personen ( personen_id SERIAL PRIMARY KEY, name TEXT NOT NULL
);
CREATE TABLE order ( order_id SERIAL PRIMARY KEY, personen_id INT REFERENCES personen
ON DELETE CASCADE ON UPDATE CASCADE NOT NULL, data TEXT
);
. Now I want to know how many orders each person has, who has at least one order. I would use the following SQL
query: select personen.personen_id, personen.text, count(order_id) from personen join orders on personen.personen_id
=orders.personen_id group by personen.personen_id, personen.text Suppose you had some more data in personen,
like10 extra fields, and you want them to be included in the result. You would have to mention each of them in the
groupby clause, not only say the personen_id. But this information that is given to the db server seems a bit
redundantto me. If the personen_id is the same (which qualifies these rows for one group), every single other field
isthe same also. Why isn't it automagically included in the group by clause? You cannot do anything useful with
thembut to group by them. select [1] from tbl1 join tbl2 on tbl1.i=tbl2.i Like: every row from tbl1 that is
mentionedas is (that is not used in an aggregate function) in the [1] marked location is automagically included in
thegroup by clause. Why?
First off, I think this query will acheive what you're looking for
SELECT * FROM personen
NATURAL JOIN
SELECT personen_id, count(order_id) AS orders FROM order GROUP BY
personen_id
Assuming of course there's no "orders" column in personen.
Enlightenment appreciated.
I believe that there was a posting on this very topic a week or two
ago. From what I recall, it's allowed under the latest SQL (98?), but
not by any of the previous flavours. Try browsing back through the
archives. :)
--
Andrew G. Hammond mailto:drew@xyzzy.dhs.org
http://xyzzy.dhs.org/~drew/
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"To blow recursion you must first blow recur" -- me
