How to take join method from user variable?

Question

MySQL

The task is to change the type of the join depending on some condition.
Set a variable according to some condition:

set @type = (SELECT CASE WHEN (подзапрос) = 0 
THEN 'left' 
ELSE 'inner' 
END)

Then use a variable.
@type JOIN table ON ...

Answer 1

Do always left join
and write in where for inner join

select a.*, b.*
from table1 a
 left join table2 b on (a.id = b.id) 
where 1=1 /*постоянное*/
and b.id is not null /*при наличии этой строки будет inner join для left join*/

Answer 2

IF (подзапрос) = 0
  SELECT … LEFT JOIN
ELSE
  SELECT … INNER JOIN