In MySQL how do I use a user defined variable in a WHERE IN clause?

Question

I don't understand why this does not work. Can someone explain what I need to do?

SET @my_list = '2,6,8,10,12,13,14,18,19,21';

DELETE FROM my_table WHERE my_table.table_id IN (@my_list);

Answer 1

It's interpreting @my_list as a single id and so you're asking it to delete from my_table where your id is the string "2,6,8,10,12,13,14,18,19,21"

You could try

SET @my_list = '2,6,8,10,12,13,14,18,19,21';
SET @exec = CONCAT('DELETE FROM my_table WHERE my_table.table_id IN (', @my_list ,')');
EXECUTE (@exec);