Re: Complicated GROUP BY

if criteria_1 and _2 are indexed:

select
  mx.product,
  p1.provider as best_provider_1,
  mx.max_criteria_1,
  p2.provider as best_provider_2
  mx.max_criteria_2
from
  (select
     product,
     max(criteria_1) as max_criteria_1,
     max(criteria_2) as max_criteria_2
   from
     products_providers group by product) mx,
   products_providers p1,
   products_providers p2
where
  p1.criteria_1=mx.max_criterial_1
  and p1.criteria_2=mx.max_criterial_2

note: you'll get a cross-product if there any ties for best provider

-----Original Message-----
From: pgsql-general-owner@postgresql.org
[mailto:pgsql-general-owner@postgresql.org] On Behalf Of dgront
Sent: Tuesday, July 08, 2008 6:12 PM
To: pgsql-general@postgresql.org
Subject: [GENERAL] Complicated GROUP BY

Dear All,

I have the following problem with grouping: I want to know the maximum
in a group as well as the maximal element. Example:

I have a table products_providers:
product  |  provider  |  criteria_1  |  criteria_2

I have a number of products, each of them from a several providers.
Each product is described by two numeric values. I can easily select
the best value for each product by a given criteria, like:

select product, max(criteria_1) from products_providers group by
product;

but I need to know the best-scoring provider as well.

Result I need should look like:
product  |  best_provider_1  | best_criteria_1  |  best_provider_2  |
best_criteria_2

If it counts results may be split into two tables: one for the first
and the other for the second criteria

Can you help me with a painless solution?
Dominik

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