一、查询数据 

ymysql-面试50题-2-CSDN博客

二、问题

31.查询课程编号为 01 且课程成绩在 80 分以上的学生的学号和姓名

mysql> select student.sid,student.sname
    -> from student,sc
    -> where cid="01"
    -> and score>=80
    -> and student.sid = sc.sid;

+------+--------+
| sid  | sname  |
+------+--------+
| 01   | 赵雷   |
| 03   | 孙风   |
+------+--------+
2 rows in set (0.00 sec)

32.求每门课程的学生人数

mysql> select sc.CId,count(*) as 学生人数
    -> from sc
    -> GROUP BY sc.CId;

+------+--------------+
| CId  | 学生人数     |
+------+--------------+
| 01   |            6 |
| 02   |            6 |
| 03   |            6 |
+------+--------------+
3 rows in set (0.00 sec)

33.成绩不重复，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩

mysql> select student.*, sc.score, sc.cid from student, teacher, course,sc
    -> where teacher.tid = course.tid
    -> and sc.sid = student.sid
    -> and sc.cid = course.cid
    -> and teacher.tname = "张三"
    -> order by score desc
    -> limit 1;

+------+--------+---------------------+------+-------+------+
| SId  | Sname  | Sage                | Ssex | score | cid  |
+------+--------+---------------------+------+-------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |  90.0 | 02   |
+------+--------+---------------------+------+-------+------+
1 row in set (0.01 sec)

34.成绩有重复的情况下，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩

mysql> select student.*, sc.score, sc.cid from student, teacher, course,sc
    -> where teacher.tid = course.tid
    -> and sc.sid = student.sid
    -> and sc.cid = course.cid
    -> and teacher.tname = "张三"
    -> and sc.score = (
    ->     select Max(sc.score)
    ->     from sc,student, teacher, course
    ->     where teacher.tid = course.tid
    ->     and sc.sid = student.sid
    ->     and sc.cid = course.cid
    ->     and teacher.tname = "张三"
    -> );

+------+--------+---------------------+------+-------+------+
| SId  | Sname  | Sage                | Ssex | score | cid  |
+------+--------+---------------------+------+-------+------+
| 01   | 赵雷   | 1990-01-01 00:00:00 | 男   |  90.0 | 02   |
+------+--------+---------------------+------+-------+------+
1 row in set (0.00 sec)

35.查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩

36.查询每门功成绩最好的前两名

37.统计每门课程的学生选修人数（超过 5 人的课程才统计）。

mysql> select sc.cid, count(sid) as cc from sc
    -> group by cid
    -> having cc >5;

+------+----+
| cid  | cc |
+------+----+
| 01   |  6 |
| 02   |  6 |
| 03   |  6 |
+------+----+
3 rows in set (0.00 sec)

38.检索至少选修两门课程的学生学号

mysql> select sid, count(cid) as cc from sc
    -> group by sid
    -> having cc>=2;

+------+----+
| sid  | cc |
+------+----+
| 01   |  3 |
| 02   |  3 |
| 03   |  3 |
| 04   |  3 |
| 05   |  2 |
| 06   |  2 |
| 07   |  2 |
+------+----+
7 rows in set (0.00 sec)

39.查询选修了全部课程的学生信息

40.查询各学生的年龄，只按年份来算

注：对于上面的一些题，后面补