Joe Celko's SQL for Smarties, 3rd Edition

27.2. Picking Random Rows from a Table

The answer is that, basically, you cannot directly pick a set of random rows from a table in SQL. There is no randomize operator in the standard, and you don’t often find the same pseudo-random number generator function in various vendor extensions, either.

Picking random rows from a table for a statistical sample is a handy thing, and you do it in other languages with a pseudo-random number generator. There are two kinds of random drawings from a set, with or without replacement. If SQL had random number functions, I suppose they would be shown as RANDOM(x) and RANDOM(DISTINCT x). But there is no such function in SQL, and none is planned. Examples from the real world include dealing a poker hand (a random ...