[pLog-svn] big LT database

Christoph Feddersen feddersen at herr-der-ringe-film.de
Tue May 2 21:44:57 GMT 2006


Exactly. Slug index needs to be kept, because the slug_id is the second
column in the multi column index. So the multi column index can't be
used to optimize something like
SELECT *
FROM blogs
where slug_id = 'XXX'

Jon Daley wrote:
>     But, we should leave the slug index?  I will read your link later -
> have to run.  When you say "left-most", you mean in the multi-column
> index listing, so that is why the slug index shouldn't be removed?
> 
> On Tue, 2 May 2006, Christoph Feddersen wrote:
> 
>> No, blog_id can be removed.
>> Why? You currently have two indexes that are indexing the blog_id column.
>> "blog_id" is a single column index and "blog_id_slug" is a multi column
>> index.
>> MySQL is able to use multi-column indexes to optimzie a query even if
>> you're using only one column in your WHERE condition. Also it has to be
>> leftmost one.
>>
>> Details:
>> http://dev.mysql.com/doc/refman/4.1/en/mysql-indexes.html
>>
>> Jon Daley wrote:
>>> I figured that was the problem.
>>>
>>> My main question was I think you said this was a bad idea:
>>>   INDEX blog_id (blog_id),
>>>   INDEX slug (slug),
>>>   INDEX blog_id_slug (blog_id,slug),
>>>
>>> That the blog_id_slug should be removed, because it doesn't do anything,
>>> correct?
>>>
>>> Thanks for your help.
>>>
>>> On Tue, 2 May 2006, Christoph Feddersen wrote:
>>>> Too much emails error -  please ask again. ;)
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> 
> **************************************
> Jon Daley
> http://jon.limedaley.com/
> 
> If you want to make enemies, try to change something.
> -- Woodrow Wilson
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