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Re: BUG #4999: select 'a' < 'A' is true, but should be false . . .

From: Peter Eisentraut <peter_e(at)gmx(dot)net>
To: Brian Ceccarelli <ceccareb(at)talussoftware(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #4999: select 'a' < 'A' is true, but should be false . . .
Date: 2009-08-24 08:53:37
Message-ID: 1251104017.10096.6.camel@vanquo.pezone.net (view raw or flat)
Thread:
Lists: pgsql-bugs
On tor, 2009-08-20 at 20:24 +0000, Brian Ceccarelli wrote:
> since the < and > comparison operators seem to be case insensitive:
> 
> select 'a' < 'Z';    -- true
> select 'a' < 'z';    -- true
> select 'A' < 'Z';    -- true
> select 'A' < 'z';    -- true
> 
> select 'z' < 'A';    -- false
> select 'z' < 'a';    -- false
> select 'Z' < 'A';    -- false
> select 'Z' < 'a';    -- false
> 
> Any case A is < any case Z implies case-insensitive compare.    Which would
> imply that 'a' = 'A', but 'a' < 'A' is true.

No, they are not "case insensitive".  The way this works is with a
multipass comparison algorithm: First, the letters are compared
independent of case, then the case is compared.  There is also an
additional pass for comparing accents, but I forget at the moment which
pass that is.  Search for Unicode collation algorithm, if you are
interested.


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