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Re: doubt about index


2015-06-22 19:47 GMT-03:00 Reindl Harald <h.reindl@xxxxxxxxxxxxx>:

> 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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