that's true if you use innodb, what about tokudb, spider, myisam and others engines? there's specific otimizations to unique keys that could be used with index that always be unique? 2015-06-22 23:08 GMT-03:00 Justin Swanhart <greenlion@gmail.com>:
Hi, the primary key is carried in secondary indexes, and PK is fastest method, these indexes make no sense. That being said, if i is unique, then i,b has to also be unique because i can never be duplicated in the table. This means that i,b is functionally dependent on the primary key, and you should just use the primary key.
--Justin
On Mon, Jun 22, 2015 at 3:53 PM, Roberto Spadim <roberto@spadim.com.br> wrote:
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 example create 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 them
yeap 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 ERP Eng. Automação e Controle
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-- Roberto Spadim SPAEmpresarial - Software ERP Eng. Automação e Controle