| From: | Josh Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | David Siegal <dsiegal(at)brave(dot)cs(dot)uml(dot)edu> |
| Cc: | pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: Calculating Percentages |
| Date: | 2003-05-14 15:24:35 |
| Message-ID: | 200305140824.35328.josh@agliodbs.com |
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| Thread: | |
| Lists: | pgsql-sql |
David,
> If I were to do:
> SELECT nationality, ((COUNT(*) * 100)/(select count(*) from member)) as
> percentage FROM member GROUP BY nationality ORDER BY nationality;
>
> would this repeatedly execute the inner query over and over?
Yes, it would
Better is:
SELECT nationality, (COUNT(*)*100/total_members) as percentage
FROM member,
(SELECT COUNT(*) as total_members FROM members) tot_mem
GROUP BY nationality
ORDER BY nationality
This method runs the grand total only once.
--
Josh Berkus
Aglio Database Solutions
San Francisco
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