Using the command:
CREATE TABLE IF NOT EXISTS `test`.`t1` (
`col` VARCHAR(16) NOT NULL
) ENGINE=MEMORY;
Running this twice in the MySQL Que
As already stated, it's a warning not an error, but (if like me) you want things to run without warnings, you can disable that warning, then re-enable it again when you're done.
SET sql_notes = 0; -- Temporarily disable the "Table already exists" warning
CREATE TABLE IF NOT EXISTS ...
SET sql_notes = 1; -- And then re-enable the warning again