That's a strange index. In InnoDB, tables are organized by primary key, so ALL indexes contain primary keys values. In other storage engines... well, I can't think a use case when that index would make sense. Maybe a more realistic example would help :) Federico -------------------------------------------- Mar 23/6/15, Roberto Spadim <roberto@spadim.com.br> ha scritto: Oggetto: Re: [Maria-discuss] doubt about index A: "Reindl Harald" <h.reindl@thelounge.net> Cc: "Maria Discuss" <maria-discuss@lists.launchpad.net> Data: Martedì 23 giugno 2015, 00:53 2015-06-22 19:47 GMT-03:00 Reindl Harald <h.reindl@thelounge.net>: Am 23.06.2015 um 00:43 schrieb Roberto Spadim: hi guys, i`m with a doubt... when i have a primary key i know that's a unique key when i have a index with primary key + any other column, does mariadb consider that it's unique too? if it is defined as unique key yes what is "index with primary key + any other column"? for examplecreate table x(i int, b int,c int, d int , e int, ... primary key(i),key teste(b,i)) the test index is primary key (i column) + any other column (b,c,d,e,...) you have two keys in that case and the select uses one of themyeap but some search algorithms use unique key/non unique key information to improve search right? does it consider that any index that contains a unique index columns + anyother column as "unique" i`m thinking more about SELECT optimization how does it matter if a key is unique or not for select optimization? select "where i=1" should return 0/1 rows (it's unique), "where b=1" should return 0+ rows, but "where b=1 and i=1" should return 0/1 rows -- Roberto Spadim SPAEmpresarial - Software ERPEng. Automação e Controle -----Segue allegato----- _______________________________________________ Mailing list: https://launchpad.net/~maria-discuss Post to : maria-discuss@lists.launchpad.net Unsubscribe : https://launchpad.net/~maria-discuss More help : https://help.launchpad.net/ListHelp