maria-discuss team mailing list archive

[Reindl Harald <h.reindl@xxxxxxxxxxxxx>]

Am 23.06.2015 um 00:53 schrieb Roberto Spadim:
> 2015-06-22 19:47 GMT-03:00 Reindl Harald <h.reindl@xxxxxxxxxxxxx
> <mailto: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,...)

these are two indexes

the second one is completly nosense as long your qquery is not in the 
form of "where b=x and i=y" and even "where i=y and b=x" won't be able 
to use it

> >  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?

which part of the documentation says that?

> does it consider that any index that contains a unique index columns +
> anyother column as "unique"

why should it?
it must not
just because they are not

>         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

it don't matter at all, these are two seperate indexes

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