Howto query for random rows?

Question

Possible Duplicate:
Alerternative to MySQL Order By Rand()

What is an efficient way to query for random result sets in the following scenarios:

• Select a single random row from many.
• Select (at least) n random rows from many.
• Select all rows in a random order.

In particular interested in MySQL, but might be a reason to try out anything else.

(Primary key is a dense AUTO_INCREMENT integer.)

Answer 1

Edit: As OMG Ponies pointed out: This doesn't scale at all. Thanks, OMG.

Try using

ORDER BY RAND()

So...

SELECT * FROM `table` ORDER BY RAND() LIMIT 1
SELECT * FROM `table` ORDER BY RAND() LIMIT n
SELECT * FROM `table` ORDER BY RAND()