maria-discuss team mailing list archive

[Reindl Harald <h.reindl@xxxxxxxxxxxxx>]

Am 23.06.2015 um 01:20 schrieb Federico Razzoli:
> I still don't understand the matter.
>
> "teste" is a unique index, because part of it is unique

no it is not *because* only a part of it is unique

> But it is not declared as unique, and MariaDB is not suppose to read our minds.

hence it is not

> The query written by Reindl looks realistic, but it would use the primary key, and I would be disappointed if it used "teste".

i won't and that is *clearly* statet in the docs

> Are we talking about real-world needs, or just speculation?

likely speculation

> --------------------------------------------
> Mar 23/6/15, Reindl Harald <h.reindl@xxxxxxxxxxxxx> ha scritto:
>
>   Oggetto: Re: [Maria-discuss] doubt about index
>   A: "Maria Discuss" <maria-discuss@xxxxxxxxxxxxxxxxxxx>
>   Data: Martedì 23 giugno 2015, 01:13
>
>
>
>   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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