问题
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.
回答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.
回答2:
For MySQL specifically:
SET @i = 0;
SELECT *
FROM users
WHERE (@i:=@i+1) < RAND()*1000
ORDER BY RAND();
来源：https://stackoverflow.com/questions/20748817/mysql-can-you-specify-a-random-limit