Re: [Maria-discuss] doubt about index

A unique index is just a btree that has a flag that says only one of these keys in the leaf. On Mon, Jun 22, 2015 at 7:13 PM, Justin Swanhart wrote:

Well, tokudb is index organized. spider uses whatever engine is remote. myisam should never be used for anything that you actually care about, aria is not stable, there are no other major engines.

On Mon, Jun 22, 2015 at 7:11 PM, Roberto Spadim wrote:

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that's true if you use innodb, what about tokudb, spider, myisam and others engines? there's specific otimizations to unique keys that could be used with index that always be unique?

2015-06-22 23:08 GMT-03:00 Justin Swanhart :

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Hi, the primary key is carried in secondary indexes, and PK is fastest method, these indexes make no sense. That being said, if i is unique, then i,b has to also be unique because i can never be duplicated in the table. This means that i,b is functionally dependent on the primary key, and you should just use the primary key.

--Justin

On Mon, Jun 22, 2015 at 3:53 PM, Roberto Spadim wrote:

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2015-06-22 19:47 GMT-03:00 Reindl Harald :

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Am 23.06.2015 um 00:43 schrieb Roberto Spadim:

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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,...)

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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"

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i`m thinking more about SELECT optimization

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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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-- Roberto Spadim SPAEmpresarial - Software ERP Eng. Automação e Controle