How to use "Case when" in "after update" trigger?

Question

JavaScript

I have an "update" trigger that looks like this:

CREATE DEFINER=`root`@`localhost` TRIGGER `Removal_add` BEFORE UPDATE ON `post_cost` FOR EACH ROW BEGIN 
set new.Removal_pl = ((CASE WHEN (select `Poli_csl` from slid where slid.id = new.id)<10 then 
 (select `Model_R_Hr` from rate where rate.id = new.id) * 
 (select `Time_hr` from rate where rate.id = new.id) * 0.3 
 else (select `Model_R_Hr` from rate where rate.id = new.id) * 
 (select `Time_hr` from rate where rate.id = new.id) END));
END

This trigger works for me, but I also want to create an "after update" trigger with the same condition from the trigger above, but I don't know how to do it, so far it gives an error.
The trigger itself:

CREATE TRIGGER post_2
    AFTER UPDATE
    ON slid FOR EACH ROW
    BEGIN 
UPDATE `harld`.`post_cost` set `Removal_pl` = CASE WHEN new.`Poli_csl`  where `id` = new.id < 10 then
 (select `Model_R_Hr` from rate where rate.id = new.id) * 
 (select `Time_hr` from rate where rate.id = new.id) * 0.3 
 else (select `Model_R_Hr` from rate where rate.id = new.id) * 
 (select `Time_hr` from rate where rate.id = new.id) END));
END;

What's wrong?

Answer 1

The second naturally!

Answer 2

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Answer 3

If for myself for the future, with the prospect of working with him in a year or two, then of course the second.
If tomorrow, in a month to work, in a project with angular, then there is most likely the first version. Therefore, it is necessary to learn first.