mysql合并 UPDATE CommunityAnswer SET agreed = agreed - 1 WHERE agreed 0 AND id = OLDanswerid AND 1 = OLDopinion; UPDATE CommunityAnswer SET opposed = opposed - 1 WHERE opposed 0 AND id = OLDanswerid

这两个MySQL语句是用于更新CommunityAnswer表中的数据。第一个语句将agreed字段减去1，条件是agreed大于0并且id等于OLD.answerid（OLD是一个MySQL关键字，表示触发器中旧的行数据），并且opinion等于1。第二个语句将opposed字段减去1，条件是opposed大于0并且id等于OLD.answerid，并且opinion等于0。这两个语句的目的是将CommunityAnswer表中的数据与触发器中的OLD行数据合并。