Question

For this (pseudo code) example I have two tables in MySQL:

member { id, name }
names { name }

There are 100 members in member and 10 names. I want to use a random name from names to update the member table. So far I’ve got this, but, not sure if there is a better method to achieve it.

UPDATE member SET name = (SELECT name FROM names ORDER BY RAND() LIMIT 1);

The code will be executed from a script so I’m looking to avoid functions etc.

Thanks in advance.

Answer 1

You could avoid ordering by rand() by adding id column to your names table and using:

UPDATE member SET name = (SELECT name FROM names WHERE id=floor(1 + rand()*10 ) );

With only 10 names the result won’t be much faster, but you would see the difference if you wanted to choose from a bigger set of names as sorting by rand() starts being inefficient quite fast and you do it for every row in members.

Update:
Seems like rand() inside where gives unpredictable results.
Use this one instead:

UPDATE member m1
JOIN ( select id, floor(1+rand()*10) as rnd from member ) m2 on m1.id=m2.id
JOIN names n on n.id = m2.rnd
SET m1.name=n.name

Number of rows affected may vary, if random name matches the one already in the table it doesnt count as update.