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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