How to use variable in MySql?

Question

MySQL

There is a small table consisting only of numbers.

SET @TEMP  := (SELECT group_concat(id) FROM world WHERE account=8);

Next, the @TEMP variable must be used in IN ().
IN (as far as I know) accepts values ​​separated by commas, so I used group_concat(id). But in the end only one value is returned

Answer 1

And here is the answer:
You can do without the variable and group_concat().
You can immediately in IN (SELECT id FROM world WHERE account=8)