Le lundi 03 octobre 2005 à 16:24 +0200, Bastian Balthazar Bux a écrit : > Yannick Warnier wrote: > > Le lundi 03 octobre 2005 à 12:29 +0200, Martijn Tonies a écrit : > > > >>>Using PhpMyAdmin, I seldom get the warning message: > >>>PRIMARY and INDEX keys should not both be set for column `ID` > >>> > >>>I understand its meaning, but I was wondering to what extent having a > >>>field indexed AND being a primary key might slow down/speed up my > >>>queries. > >>> > >>>Is that gonna take twice the time if I am searching on the ID field, > >>>just because there are two indexes? > >>> > >>>I'd like to have a rough idea of how serioulsy I need to avoid these. > >> > >>Creating a PRIMARY KEY will automatically create an index. > >> > >>Why would you create a second index for that field? > > > > > > I'm asking myself the same question. I am working on someone else's > > database. > > > > Thanks both, > > > > Yannick > > > > > > > Is it a multi-field index ? some versions of phpmyadmin show that > messages also if only one field is duplicated. > > example: > > > CREATE TABLE `tab_sint` ( > `id_cns` tinyint(3) unsigned NOT NULL default '0', > `anno_dep` smallint(4) unsigned zerofill NOT NULL default '0000', > `data_dep` smallint(4) unsigned zerofill NOT NULL default '0000', > `particolare` mediumint(8) unsigned NOT NULL default '0', > `generale` mediumint(8) unsigned NOT NULL default '0', > UNIQUE KEY `idx_cns_gen_anno` > (`anno_dep`,`id_cns`,`generale`,`particolare`), > UNIQUE KEY `idx_cns_par_anno` > (`id_cns`,`anno_dep`,`tipo`,`particolare`,`bis`) > ) ENGINE=MyISAM DEFAULT CHARSET=utf8 PACK_KEYS=1 AUTO_INCREMENT=87189031 ; > > > This schema issue the warning on 'id_cns' but really make sense having 2 > indices here since they serves different kind of querys and constraints.
No, no, it's just a dumb double index :-) I am pretty sure it is completely useless. Actually I have already removed it. Yannick -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
