database - adding a trigger in mysql to change a content on update -

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i want add mysql trigger on update function. should triggered on updating specific column of 1 table 'available teachers' , update specific column of table 'available subjects'. how achievable?

i believe checking change in old , new field after update of teachers table update available column of subjects it.

if not (new.teachers.available <=> old.teachers.available)   set new.subject.available = new.teachers.available; end if;;

it should right?


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