当UNIQUE约束被作用的Sname字段时，如下语句将会更改王二麻子同学的年龄为21岁，它会对Student表做出 0 或 1 行的更改。UPDATE StudentSET Sage = 21WHERE Sname = '王二麻子';

下面SQL语句中，用于删除student表中age小于20的记录的语句是 A: DELETE student where age<20; B: DELETE FROM student where age<20; C: DELETE FROM student set age<20; D: DELETE studentset age<20;