MySQL subselect performance question

mysqloptimizationsubquery

I need advice regarding subselect performance in MySQL. For a reason that I can't change, I am not able to use JOIN to create quesry filter, I can only add another AND clause in WHERE.

What is the peformance of:

select tasks.*
from tasks
where 
  some criteria
  and task.project_id not in (select id from project where project.is_template = 1);

compared to:

select tasks.*
from tasks, project
where
  some criteria
  and task.project_id = project.id and project.is_template <> 1;

Note that there is relatively small number of projects whete is_template = 1, and there could be large number of projects where is_template <> 1.

Is there other way to achieve the same result without subselects if I can't change anything but and filter?

Best Solution

I believe that the second is more efficient as it requires only one select, but to be sure, you should EXPLAIN each query and check the results.

EXPLAIN select tasks.*
from tasks
where 
  some criteria
  and task.project_id not in (select id from project where project.is_template = 1);

EXPLAIN select tasks.*
from tasks, project
where
  some criteria
  and task.project_id = project.id and project.is_template <> 1;