mysql 觸發器

添加

CREATE TRIGGER 觸發名稱 BEFORE 關鍵字 ON 表名  FOR EACH ROW
BEGIN
    IF new.much > (SELECT gnum FROM g WHERE gname=new.gname) THEN
    SET new.much = (SELECT gnum FROM g WHERE gname=new.gname);
    UPDATE g SET gnum=gnum-new.much WHERE gname=new.gname;
ELSE
    UPDATE g set gnum=gnum-new.much WHERE gname=new.gname;
END IF;
END;

修改

CREATE TRIGGER up BEFORE UPDATE ON o FOR EACH ROW

BEGIN
    IF new.much > ((SELECT gnum FROM g WHERE gname=new.gname)+old.much) THEN
    SET new.much = ((SELECT gnum FROM g WHERE gname=new.gname)+old.much);
    UPDATE g SET gnum=gnum+old.much-new.much WHERE gname=new.gname;
ELSE
    UPDATE g SET gnum=gnum+old.much-new.much WHERE gname=new.gname;
END IF;
END;

刪除觸發器

DROP TRIGGER 觸發名稱;