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Asked: 2026-05-10T23:24:58+00:00

I need advice regarding subselect performance in MySQL. For a reason that I can’t

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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?

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1 Answer

  1. 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;
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