Need help creating a trigger

[Rob Rowsome]

I am trying to create a trigger that updates a different table on insert.

create trigger recalc_post_count after insert on posting
update thread set post_count = (select count(*) from posting where thread_id = new.thread_id) where thread_id = new.thread_id;

I get this error message: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'update thread set post_count = (select count(*) from posting where thread_id = n' at line 2

I'm using MySQL version 5.045

Why won't this work? Am I not allowed to update a different table from the one the trigger is on?

Thanks,
Rob