Question

写出下面相应的SQL语句 有两个数据库表，字段分别如下：

1）查询所有年龄在18到20岁之间的学生总人数

2）查谗“王欢”同学“数据结构”的成绩。

3）求所有学生的“数据结构”平均分

4）把“王欢”同学的年龄修为21岁

5）删除学生成绩表

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Answer 1

1
select count(*) from student where age between 18 and 20

2
select student_score.score
from student,student_score where student.id=student_score.id and student.name='王欢'
and student_score.km_name='数据结构'

3
select avg(student_score.score) as 平均成绩
from student,student_score where student.id=student_score.id and student_score.km_name='数据结构'

4
update student set age=21 where name='王欢'

5
delete from student_score