mysql - Select if exist else insert?

Question

IF EXISTS (select * from users where username = 'something') THEN
    select id from users where username = 'something';
ELSE 
    insert into users (username) values ('something');
END IF;

Answer 1

Your statement is fine as it is. Only problem is, you can't use it like a normal query. Control structures like IF or WHILE are only allowed in stored procedures or functions.

Just create a procedure like this:

delimiter $$

create procedure select_or_insert()
begin

IF EXISTS (select * from users where username = 'something') THEN
    select id from users where username = 'something';
ELSE 
    insert into users (username) values ('something');
END IF;

end $$

and call it like this:

call select_or_insert();

That's it.