maria-discuss team mailing list archive

[Justin Swanhart <greenlion@xxxxxxxxx>]

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 <roberto@xxxxxxxxxxxxx>
wrote:

> 2015-06-22 19:47 GMT-03:00 Reindl Harald <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,...)
>
>
>
>
>> 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"
>
>
>>
>>
>>  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
>
>
>
> --
> Roberto Spadim
> SPAEmpresarial - Software ERP
> Eng. Automação e Controle
>
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