On Tue, Apr 29, 2008 at 7:39 AM, C.R.Vegelin <cr.vegelin@hetnet.nl> wrote:
> ----- Original Message ----- From: "Rob Wultsch" <wultsch@gmail.com>
> To: "C.R.Vegelin" <cr.vegelin@hetnet.nl>
> Cc: <mysql@lists.mysql.com>
> Sent: Tuesday, April 29, 2008 2:24 PM
> Subject: Re: why is explain.key-len not size of key field ?
>
>
>
>
>
> > On Tue, Apr 29, 2008 at 5:12 AM, C.R.Vegelin <cr.vegelin@hetnet.nl> wrote:
> >
> > > Hi All,
> > >
> > > I have a dictionary table like:
> > > CREATE TABLE IF NOT EXISTS `mydictionary`
> > > (
> > > `EN` varchar(36) default NULL,
> > > `DE` varchar(36) default NULL,
> > > `ES` varchar(36) default NULL,
> > > `FR` varchar(36) default NULL,
> > > `IT` varchar(36) default NULL,
> > > `NL` varchar(36) default NULL,
> > > `PT` varchar(36) default NULL,
> > > KEY `EN` (`EN`),
> > > KEY `DE` (`DE`),
> > > KEY `ES` (`ES`),
> > > KEY `FR` (`FR`),
> > > KEY `IT` (`IT`),
> > > KEY `NL` (`NL`),
> > > KEY `PT` (`PT`)
> > > ) ENGINE=MyISAM DEFAULT CHARSET = UTF8;
> > >
> > > When I run the query:
> > > EXPLAIN SELECT `EN`, `FR` FROM `mydictionary`
> > > WHERE `FR` Like "comp%" ORDER BY `FR`;
> > >
> > > EXPLAIN says:
> > > select type = SIMPLE, type = range, key = FR,
> > > key-len = 111, ref = NULL, extra = using where
> > >
> > > Any idea why key-len is 111 ?
> > >
> > > Thanks, Cor
> > >
> > >
> >
> > Your using a multi byte character set.
> >
> > Rob Wultsch
> > wultsch@gmail.com
> >
> >
>
> Thanks Rob,
>
> So key-len is expressed in bytes and not in characters.
> But that means that each normal character (a..z) is 3 bytes in UTF8 ?
>
> TIA, Cor
>
>
Max memory usage is 3 bytes in MySQL. I am not an expert on this
subject. Take a look at the following:
http://en.wikipedia.org/wiki/UTF-8
http://www.xaprb.com/blog/2006/04/17...ngth-in-mysql/

--
Rob Wultsch
wultsch@gmail.com
wultsch (aim)