更新表student中字段grade的值，使其在原来基础上加20分但不能超出100的限制，能够完成上述要求的SQL语句是（ ）
ALTER TABLE student set grade=grade+20;
B. UPDATE student set grade=grade+20 where grade<=80; UPDATE student set grade=100;
C. UPDATE student set grade=grade+20 ; UPDATE student set grade=100 where grade>100;
D. UPDATE student set grade=grade+20; UPDATE student set grade=100;
下列选项中，与INSERT INTO student SET id=5,name='boya',grade=99;功能相同的SQL语句是（ ）
A. INSERT INTO student(id,name, grade)VALUES(5, 'boya', 99);
B. INSERT INTO student VALUES('youjun',5,99);
C. INSERT INTO student(id,‘grade’,’name’)VALUES(5,’boya’,99);
D. INSERT INTO student(id,grade,’name’)VALUES(5,99,”boya”);
将student表按照gender字段进行分组查询，查询出grade字段值之和小于300的分组，依据上述要求，下面选项中，正确的SQL语句是（）
A. SELECT sum(grade),gender FROM student GROUP BY gender HAVING SUM(grade)<300;
B. SELECT sum(grade),gender FROM student GROUP BY gender WHERE SUM(grade)<300;
C. SELECT sum(grade),gender FROM student WHERE SUM(grade)<300 GROUP BY gender;
D. 以上语句都不对
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