When you want to look up a specific word in a 500-page paper tome, where do
you look? That''s the same idea as database indexes =)
On Thu, Jul 7, 2011 at 09:04, Walter Lee Davis
<waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org> wrote:
>
> On Jul 7, 2011, at 7:28 AM, Rodrigo Ruiz wrote:
>
> What is add_index for?
>>
>> Someone told me it was to add indexes to the database, but I still dont
>> know what indexes are... first I thought they where other columns of
the
>> table, but apparently not.
>>
>
> Indexes are a feature of the relational database. One way they work is to
> organize common query features (sort by date added, for example) in the
> database''s structure so that they can happen much more quickly
than a simple
> brute-force approach could do. Other types of indexes can enforce
uniqueness
> (only one copy of this e-mail address may be added ever) at a fundamental
> level.
>
> Adding an index to a column can return dramatic speed improvements on
> reads, at the expense of slightly longer write times. Like anything,
it''s a
> trade-off.
>
> Like anything to do with the raw database design, you''ll have to
read up on
> the specifics of your particular RDBMS to figure out which sort of index
> structure makes the most sense for your application. If you have access to
> someone who is a DBA, they can tell you lots of useful tricks that you
might
> use.
>
> But always, add an index (for speed) when you are tuning, not before. An
> index for uniqueness you can add if it makes sense in your design.
>
> Walter
>
>
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