MySQL: Can you specify a random limit?

Question

Is there a way to randomize a limit number in SQL (MySQL)?

What I'd like to be able to do is get a random number of results in a query to use in an insertion subquery without any server-side scripting. The query I'd love to be able to run as a hypothetical illustration is:

SELECT id FROM users ORDER BY RAND() LIMIT RAND() * 1000

Of course that doesn't work, but is there another way to randomize the limit number? There are plenty of examples of randomizing a limited set of results, but I can't find anything on the net about setting a random limit.

Answer 1

How about this:

    SELECT * 
      FROM users
     ORDER BY RAND()
     HAVING RAND() * 1000 < 10

The clause WHERE RAND() * 1000 < 10 randomly chooses to include each row with a probability of 1%. It's not quite a LIMIT variable clause but will do roughly the same thing.

Answer 2

For MySQL specifically:

SET @i = 0;
SELECT * 
FROM users
WHERE (@i:=@i+1) < RAND()*1000
ORDER BY RAND();