Re: [PERFORM] Query performance

Bill wrote:
```Ok, thanks.  So let me explain the query number 2 as this is the more
difficult to write.  So I have a list of stocks, this table contains the
price of all of the stocks at the open and close date.  Ok, now we have a
ratio from query (1) that returns at least a very rough index of the daily
performance of a given stock, with each ratio representing the stock's
performance in one day.  Now we need to average this with the same stock's
ratio every day, to get a total average for each stock contained in the
database.  Now I would simply like to find a ratio like this that represents
the average of every stock in the table and simply find the greatest ratio.
Sorry about the lousy explanation before, is this a bit better?

```

`Here is an example if needed.`

`Say we have a stock by the name of YYY`

```I know, due to query 1 that stock YYY has a abs(close-open)/open price ratio
of for example, 1.3 on Dec 1 and (for simplicity let's say we only have two
dates) and Dec 2 the ratio for YYY is 1.5. So the query averages and gets
1.4.  Now it needs to do this for all of the stocks in the table and sort by
increasing ratio.
```
`Well, the simplest would be something like:`

CREATE VIEW my_ratios AS SELECT ...(select details we used for #1 previously)

```Query #1 then becomes:
SELECT * FROM my_ratios;```

```Then you could do:
SELECT
symbol,
avg(ratio) as ratio_avg
FROM
my_ratios
GROUP BY
symbol
ORDER BY
avg(ratio)
;```

Now, in practice, I'd probably create a symbol_ratio table and fill that one day at a time. Then #2,#3 would be easier.

```--
Richard Huxton
Archonet Ltd```

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