Retreive Random Unique REcords from SQL

[Count]

G'day, i'm trying to create a page that retreives up to 15 random records out of an SQL table to be displayed to a user, at the same time, they cannot be duplicates.

I dont quite know how to go about doing this effectivly. One method i was trying to use included nesting a while loop in a for loop to determine if each record retreived has a unique ID, but that led to a dead end with infinite loops.

Can someone point me in the direction of the best method for going about this?

[laserlight]

The easy way would be to use:

SELECT column FROM table ORDER BY RAND() LIMIT 15

However this might be slow for large tables, since the way it probably works is to shuffle entire table then select the first 15 rows.

[Sxooter]

Assuming you have some unique int column there, you could also use php's random function to generate 15 random numbers in the range of the unique int column, removing any dups in the php 'verse before throwing them at the db. Note that if you have holes in your int pk you'd have to account for that as well.

Is this a big set or a small one? If a small one, then laserlight's method is preferred, as you don't have to worry about holes in your sequence.