MS SQL Trigger更新调用死锁？

I have two tables. Club and Coach. Between them is 0,1 - 0,1 relationship (coach can have zero or one club. club can have zero or one coach). When I want to change the coach of the given club, i have to update the club table. So i have to change idCoach of that club. Lets consider a new coach (the newly assigned coach of the given club) is already a coach of some other club. I have to set to Null field idCoach of that club, because his coach will be assigned to another club. Also if the club for which I want to change the coach, already has a coach, then I have to set idClub of that coach (in Coach table) to Null.I have two tables. Club and Coach. Between them