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Re: Query performance

From: "Mischa Sandberg" <mischa_sandberg(at)telus(dot)net>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Query performance
Date: 2004-06-28 05:23:53
Message-ID: JXNDc.27548$_5.7680@clgrps13 (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Usually, when you post a request like this, you should provide something a little more concrete (the CREATE TABLE statement for that table, with 
Since you didn't, I'll posit something that sounds like what you're using, and take a stab at your problem.

TABLE Prices (
    stock    VARCHAR(9)
    ,asof         DATE,
    ,opening   MONEY
    ,closing    MONEY
    ,PRIMARY KEY (stock, asof)

SELECT    stock, AVG((closing-opening)/opening) as ratio
FROM    Prices 
GROUP BY stock
ORDER BY ratio DESC LIMIT 10;    -- top 10 best-performing stocks.

""Bill"" <bill(at)math(dot)uchicago(dot)edu> wrote in message news:BILLSA1XvpFVjCRGryW00000002(at)bill(dot)fefferman(dot)org(dot)(dot)(dot)
  Actually, I have some queries that are slow, however I was wondering if you could help me write a query that is rather simple, but I, as a true database novice, can't seem to conjure.  So we have stocks, as I have previously said, and I have a huge table which contains all of the opening and closing prices of some stocks from each day.  What I like to do, in English, for each stock in each day is find a ratio: abs(closing-opening)/opening.  Then I would like to average all of the ratios of each day of each individual stock together to find a final ratio for each stock, then I would like to find the highest average, to find the best performing stock.  So what query can I use, and (as is appropriate for this group), how can it be optimized to run the fastest?


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