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Re: doubt about index


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
  > 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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