--12.创建表 studentgrad(sno,mathgrade,englishigrade,chinesegrade) 计算学生各科总成绩并赋予别名create table studentgrade(sno char(8) primary key,mathgrade tinyint,englishgrade tinyint,chinesegrade tinyint)insert into studentgrade(sno,mathgrade,englishgrade,chinesegrade) values( '95001',85,95,74)i...