maria-discuss team mailing list archive

[Roberto Spadim <roberto@xxxxxxxxxxxxx>]

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 <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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>


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