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Re: doubt about index


I still don't understand the matter.

"teste" is a unique index, because part of it is unique. But it is not declared as unique, and MariaDB is not suppose to read our minds.

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

Are we talking about real-world needs, or just 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
 > 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
 > )
 > 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
 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
 it don't
 matter at all, these are two seperate indexes
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