Re: Doubt about join clause

You've understood very well my problem, but also this query works as worse
than everything I did before, it throws as many rows as rows are contained
my tables clients and stores. I only want to find for every client what
store is closer to him, I expect one client to one store and their distance

Thanks a lot

Bill Moran wrote:
>
> In response to jc_mich <juan(dot)michaca(at)paasel(dot)com>:
>>
>> Hello
>>
>> I have a table with clients and other with stores, I want to calculate
>> minimum distances between stores and clients, the client name and its
>> closer
>> store.
>>
>> At this moment I can only get clients ids and minimum distances grouping
>> by
>> client id, but when I try to join their respective store id, postgres
>> requires me to add store id in group clause and it throws as many rows as
>> the product of number clients and stores. This result is wrong, I only
>> expect the minimum distance for every client.
>>
>> My code looks like this:
>>
>> SELECT distances.client_id, min(distances.distance) FROM(
>> SELECT stores.id AS store_id, clients.id AS client_id,
>> sqrt(power(store.x)+power(store.y)) AS distance
>> FROM stores, clients
>> WHERE 1=1
>> ORDER BY stores.id, dist) AS distances GROUP BY distances.client_id;
>>
>> Also I've tried this:
>> SELECT clients.id, MIN(distances.distance)
>> FROM stores, clients LEFT JOIN(SELECT clients.id AS client_id, stores.id,
>> sqrt(power(stores.x)+power(stores.y)) AS distance
>> FROM stores, clients
>> WHERE 1=1) distances
>> ON distances.client_id = clients.id GROUP BY clients.id
>>
>> Thanks in advance!
>
> Something like this should work, (assuming I understand your tables):
>
> SELECT clients.id, stores.id,
> min(sqrt(power(clients.x-stores.x)+power(clients.y-stores.y))
> FROM clients, stores
> GROUP BY clients.id, stores.id;
>
> --
> Bill Moran
> http://www.potentialtech.com
> http://people.collaborativefusion.com/~wmoran/
>
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