Parentheses and joins

From: Jonathan Gennick <jonathan_at_gennick.com>
Date: Wed, 10 Dec 2003 10:54:30 -0800
Message-ID: <F001.005D972E.20031210105430@fatcity.com>

I looking for a good, simple example of when parentheses matter when writing a join query using the new, SQL92 join syntax. For example, I could write:

SELECT *
FROM county y JOIN city c

     ON y.county_id = c.county_id
     JOIN attraction a
     ON c.city_id = a.city_id;

and I could use parens to clarify the join order:

SELECT *
FROM (county y JOIN city c

     ON y.county_id = c.county_id)
     JOIN attraction a
     ON c.city_id = a.city_id;

I could even force a different join order:

SELECT *
FROM county y JOIN (city c

     JOIN attraction a
     ON c.city_id = a.city_id)
     ON y.county_id = c.county_id;

I'm struggling to come up with a good example of when you might *need* to use parens. I'm not having a really good day today. In fact, I'm having a really, really bad day, so maybe I'm not thinking too clearly, but so far I'm unable to come up with a good example to demonstrate the necessity of parentheses. Can anyone help me out with this?

Best regards,

Jonathan Gennick --- Brighten the corner where you are http://Gennick.com * 906.387.1698 * mailto:jonathan@gennick.com

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Author: Jonathan Gennick
  INET: jonathan_at_gennick.com

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