一、查询数据
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