表关系
查询练习
1、自行创建测试数据; 2、查询学生总人数; 3、查询“生物”课程和“物理”课程成绩都及格的学生id和姓名; 4、查询每个年级的班级数,取出班级数最多的前三个年级; 5、查询平均成绩最高和最低的学生的id和姓名以及平均成绩; 6、查询每个年级的学生人数; 7、查询每位学生的学号,姓名,选课数,平均成绩; 8、查询学生编号为“2”的学生的姓名、该学生成绩最高的课程名、成绩最低的课程名及分数; 9、查询姓“李”的老师的个数和所带班级数; 10、查询班级数小于5的年级id和年级名; 11、查询班级信息,包括班级id、班级名称、年级、年级级别(12为低年级,34为中年级,56为高年级),示例结果如下; 班级id 班级名称 年级 年级级别 1 一年一班 一年级 低 12、查询学过“张三”老师2门课以上的同学的学号、姓名; 13、查询教授课程超过2门的老师的id和姓名; 14、查询学过编号“1”课程和编号“2”课程的同学的学号、姓名; 15、查询没有带过高年级的老师id和姓名; 16、查询学过“张三”老师所教的所有课的同学的学号、姓名; 17、查询带过超过2个班级的老师的id和姓名; 18、查询课程编号“2”的成绩比课程编号“1”课程低的所有同学的学号、姓名; 19、查询所带班级数最多的老师id和姓名; 20、查询有课程成绩小于60分的同学的学号、姓名; 21、查询没有学全所有课的同学的学号、姓名; 22、查询至少有一门课与学号为“1”的同学所学相同的同学的学号和姓名; 23、查询至少学过学号为“1”同学所选课程中任意一门课的其他同学学号和姓名; 24、查询和“2”号同学学习的课程完全相同的其他同学的学号和姓名; 25、删除学习“张三”老师课的score表记录; 26、向score表中插入一些记录,这些记录要求符合以下条件:①没有上过编号“2”课程的同学学号;②插入“2”号课程的平均成绩; 27、按平均成绩从低到高显示所有学生的“语文”、“数学”、“英语”三门的课程成绩,按如下形式显示: 学生ID,语文,数学,英语,有效课程数,有效平均分; 28、查询各科成绩最高和最低的分:以如下形式显示:课程ID,最高分,最低分; 29、按各科平均成绩从低到高和及格率的百分数从高到低顺序; 30、课程平均分从高到低显示(显示任课老师); 31、查询各科成绩前三名的记录(不考虑成绩并列情况) 32、查询每门课程被选修的学生数; 33、查询选修了2门以上课程的全部学生的学号和姓名; 34、查询男生、女生的人数,按倒序排列; 35、查询姓“张”的学生名单; 36、查询同名同姓学生名单,并统计同名人数; 37、查询每门课程的平均成绩,结果按平均成绩升序排列,平均成绩相同时,按课程号降序排列; 38、查询课程名称为“数学”,且分数低于60的学生姓名和分数; 39、查询课程编号为“3”且课程成绩在80分以上的学生的学号和姓名; 40、求选修了课程的学生人数 41、查询选修“王五”老师所授课程的学生中,成绩最高和最低的学生姓名及其成绩; 42、查询各个课程及相应的选修人数; 43、查询不同课程但成绩相同的学生的学号、课程号、学生成绩; 44、查询每门课程成绩最好的前两名学生id和姓名; 45、检索至少选修两门课程的学生学号; 46、查询没有学生选修的课程的课程号和课程名; 47、查询没带过任何班级的老师id和姓名; 48、查询有两门以上课程超过80分的学生id及其平均成绩; 49、检索“3”课程分数小于60,按分数降序排列的同学学号; 50、删除编号为“2”的同学的“1”课程的成绩; 51、查询同时选修了物理课和生物课的学生id和姓名;
建立相关表
create table class_grade( gid int primary key auto_increment, gname varchar(16) not null unique ); create table class( cid int primary key auto_increment, caption varchar(16) not null, grade_id int not null, foreign key(grade_id) references class_grade(gid) ); create table student( sid int primary key auto_increment, sname varchar(16) not null, gender enum('女','男') not null default '女', class_id int not null, foreign key(class_id) references class(cid) ); create table teacher( tid int primary key auto_increment, tname varchar(16) not null ); create table course( cid int primary key auto_increment, cname varchar(16) not null, teacher_id int not null, foreign key(teacher_id) references teacher(tid) ); create table score( sid int not null unique auto_increment, student_id int not null, course_id int not null, score int not null, primary key(student_id,course_id), foreign key(student_id) references student(sid) on delete cascade on update cascade, foreign key(course_id) references course(cid) on delete cascade on update cascade ); create table teach2cls( tcid int not null unique auto_increment, tid int not null, cid int not null, primary key(tid,cid), foreign key(tid) references teacher(tid) on delete cascade on update cascade, foreign key(cid) references class(cid) on delete cascade on update cascade ); 建表
添加测试数据
# 5 个年级 insert into class_grade(gname) values ('一年级'), ('二年级'), ('三年级'), ('四年级'), ('五年级'); # 5 个老师 insert into teacher(tname) values ('张三'), ('李四'), ('王五'), ('李杰'), ('赵六'); # 12 个班级 insert into class(caption,grade_id) values ('一年一班',1), ('一年二班',1), ('一年三班',1), ('一年四班',1), ('一年五班',1), ('二年一班',2), ('二年二班',2), ('三年一班',3), ('三年二班',3), ('四年一班',4), ('四年二班',4), ('五年一班',5); # 10 个课程 insert into course(cname,teacher_id) values ('生物',1), ('体育',1), ('物理',2), ('化学',3), ('美术',4), ('音乐',2), ('语文',3), ('数学',4), ('地理',2), ('研究',1); # 18 个学生 insert into student(sname,gender,class_id) values # 12个学生 ('孙尚香','女',1), ('貂蝉','女',1), ('刘备','男',2), ('孙二娘','女',2), ('张飞','男',3), ('关羽','男',4), ('林黛玉','女',5), ('薛宝钗','女',6), ('宋江','男',6), ('白骨精','女',7), ('猪八戒','男',8), ('王熙凤','女',1), ('李师师','女',2), ('金翠莲','女',9), ('如花','女',1), ('沙僧','男',2), ('李美丽','女',3), ('金角大王','男',4); insert into score(student_id,course_id,score) values (1,1,60), (1,2,59), (1,3,58), (1,4,22), (1,5,59), (1,6,60), (1,7,99), (1,8,100), (1,9,88), (2,1,99), (2,2,99), (2,3,89), (2,4,60), (2,5,59), (2,6,33), (2,7,56), (2,8,59), (2,9,60), (3,1,59), (3,3,30), (3,5,28), (3,7,70), (3,9,60), (4,2,59), (4,4,100), (4,6,90), (4,8,80), (4,10,88), (5,1,59), (5,2,33), (5,3,12), (5,4,88), (6,1,60), (6,3,99), (6,5,100), (6,6,60), (6,7,59), (6,8,100), (6,9,88), (7,9,20), (7,1,36), (7,3,57), (7,5,60), (7,8,60), (7,10,60), (8,2,61), (8,4,59), (8,6,62), (9,8,59), (9,1,60), (9,2,61), (9,3,21), (10,1,70), (10,3,88), (10,5,68), (10,9,99), (11,1,89), (11,7,99), (12,3,100), (12,8,60); insert into teach2cls(tid,cid) values (1,1), (1,2), (1,3), (1,5), (2,4), (2,6), (2,8), (2,9), (2,1), (2,5), (3,7), (3,1), (3,3), (3,5), (3,9), (4,7), (4,2), (4,4), (4,6), (4,8), (4,1), (1,12), (2,12);
参考SQL
1、自行创建测试数据; 详见"db5_结构+数据.sql" 2、查询学生总人数; select count(sid) from student ; 3、查询“生物”课程和“物理”课程成绩都及格的学生id和姓名; select sid, sname from student where sid in( select score.student_id from score inner join course on score.course_id=course.cid where course.cname in( '生物', '物理' ) and score.score >= 60 group by score.student_id having count(course_id)=2 ); 4、查询每个年级的班级数,取出班级数最多的前三个年级; select gname from class_grade where gid in ( select grade_id from class group by grade_id having count(cid) in ( select t1.count_cid from ( select distinct count(cid) as count_cid from class group by grade_id order by count_cid desc limit 3 ) as t1 ) ); 5、查询平均成绩最高和最低的学生的id和姓名以及平均成绩; select student.sid, student.sname, t1.avg_score from student inner join ( select student_id, avg(score) as avg_score from score group by student_id having avg(score) in ( ( select avg(score) as max_avg_score from score group by student_id order by avg(score) desc limit 1 ), ( select avg(score) as min_avg_score from score group by student_id order by avg(score) asc limit 1 ) ) ) as t1 on student.sid = t1.student_id; 6、查询每个年级的学生人数; select t1.grade_id, count(t1.sid) as count_student from ( select student.sid, class.grade_id from student inner join class on student.class_id=class.cid ) as t1 group by t1.grade_id; 7、查询每位学生的学号,姓名,选课数,平均成绩; select student.sid, student.sname, t1.count_course, t1.avg_score from student left join ( select student_id, count(course_id) as count_course, avg(score) as avg_score from score group by student_id ) as t1 on student.sid = t1.student_id; 8、查询学生编号为“2”的学生的姓名、该学生成绩最高的课程名、成绩最低的课程名及分数; select student.sname, course.cname, t1.score from( select student_id, course_id, score from score where student_id=2 and score in( ( select min(score) from score where student_id=2 ), ( select max(score) from score where student_id=2 ) ) ) as t1 inner join student on t1.student_id=student.sid inner join course on t1.course_id=course.cid; 9、查询姓“李”的老师的个数和所带班级数; select teacher.tid, teacher.tname, t1.count_cid from teacher left join ( select tid, count(cid) as count_cid from teach2cls where tid in ( select tid from teacher where tname like '李%' ) group by tid ) as t1 on teacher.tid = t1.tid where teacher.tname like '李%'; 10、查询班级数小于5的年级id和年级名; select gid, gname from class_grade where gid in ( select grade_id from class group by grade_id having count(caption)<5 ); 11、查询班级信息,包括班级id、班级名称、年级、年级级别(12为低年级,34为中年级,56为高年级),示例结果如下; 班级id 班级名称 年级 年级级别 1 一年一班 一年级 低 # case when ... then select class.cid 班级id, class.caption 班级名称, class_grade.gname 年级, case when class_grade.gid between 1 and 2 then '低' when class_grade.gid between 3 and 4 then '中' when class_grade.gid between 5 and 6 then '高' else 0 end as '年级级别' from class, class_grade where class.grade_id = class_grade.gid; 12、查询学过“张三”老师2门课以上的同学的学号、姓名; select sid, sname from student where sid in ( select student_id from score where course_id in ( select course.cid from teacher, course where teacher.tid = course.teacher_id and teacher.tname = '张三' ) group by student_id having count(course_id) > 2 ); 13、查询教授课程超过2门的老师的id和姓名; select tid, tname from teacher where tid in ( select teacher_id from course group by teacher_id having count(cid) > 2 ); 14、查询学过编号“1”课程和编号“2”课程的同学的学号、姓名; select sid, sname from student where sid in ( select distinct student_id from score where course_id in ( 1, 2 ) ); 15、查询没有带过高年级的老师id和姓名; select tid, tname from teacher where tid not in ( select tid from teach2cls where cid in ( select cid from class where grade_id in ( 5, 6 ) ) ); 16、查询学过“张三”老师所教的所有课的同学的学号、姓名; select sid, sname from student where sid in ( select student_id from score inner join course on score.course_id=course.cid where teacher_id in( select sid from teacher where sname='张三' ) ) 17、查询带过超过2个班级的老师的id和姓名; select tid, tname from teacher where tid in ( select teacher_id from course group by teacher_id having count(cid) > 2 ); 18、查询课程编号“2”的成绩比课程编号“1”课程低的所有同学的学号、姓名; select sid, sname from student where sid in ( select t1.student_id from ( select student_id, score from score where course_id = 2 group by student_id ) as t1, ( select student_id, score from score where course_id = 1 group by student_id ) as t2 where t1.student_id = t2.student_id and t1.score < t2.score ); 19、查询所带班级数最多的老师id和姓名; # 考虑班级数并列最多的情况 select tid, tname from teacher where tid in ( select tid from teach2cls group by tid having count(cid) = ( select count(cid) from teach2cls group by tid order by count(cid) desc limit 1 ) ); 20、查询有课程成绩小于60分的同学的学号、姓名; select sid, sname from student where sid in ( select distinct student_id from score where score < 60 ); 21、查询没有学全所有课的同学的学号、姓名; select sid, sname from student where sid not in ( select student_id from score group by student_id having count(course_id) = ( select count(cid) from course ) ); 22、查询至少有一门课与学号为“1”的同学所学相同的同学的学号和姓名; select sid, sname from student where sid in ( select student_id from score where course_id in ( select course_id from score where student_id = 1 ) group by student_id ); 23、查询至少学过学号为“1”同学所选课程中任意一门课的其他同学学号和姓名; select sid, sname from student where sid in ( select student_id from score where course_id in ( select course_id from score where student_id = 1 ) group by student_id ) and sid != 1; 24、查询和“2”号同学学习的课程完全相同的其他同学的学号和姓名; select sid, sname from student where sid in ( select score.student_id from score, ( select course_id from score where student_id = 2 ) as t1 where score.course_id = t1.course_id and score.student_id != 2 group by score.student_id having count(score.course_id) = ( select count(course_id) from score where student_id = 2 ) ); 25、删除学习“张三”老师课的score表记录; delete from score where course_id in ( select course.cid from course, teacher where course.teacher_id = teacher.tid and teacher.tname = '张三' ); 26、向score表中插入一些记录,这些记录要求符合以下条件:①没有上过编号“2”课程的同学学号;②插入“2”号课程的平均成绩; # 实际结果会和上面一题有冲突,张三老师所教的2号课程 insert into score(student_id,course_id,score) select t1.sid, 2, t2.avg_score from ( select sid from student where sid not in ( select student_id from score where course_id = 2 ) ) as t1, ( select avg(score) as avg_score from score where course_id = 2 ) as t2; 27、按平均成绩从低到高显示所有学生的“语文”、“数学”、“英语”三门的课程成绩,按如下形式显示: 学生ID,语文,数学,英语,有效课程数,有效平均分; # 有效成绩含所有课程,包括语数英 select t1.student_id as 学生ID, (select score.score from score left join course on score.course_id = course.cid where course.cname = '语文' and score.student_id = t1.student_id) as 语文, (select score.score from score left join course on score.course_id = course.cid where course.cname = '数学' and score.student_id = t1.student_id) as 数学, (select score.score from score left join course on score.course_id = course.cid where course.cname = '音乐' and score.student_id = t1.student_id) as 英语, count(t1.course_id) as 有效课程数, avg(t1.score) as 有效平均分 from score as t1 group by t1.student_id order by avg(t1.score) asc; 28、查询各科成绩最高和最低的分:以如下形式显示:课程ID,最高分,最低分; select course.cid as 课程ID, max(score.score) as 最高分, min(score.score) as 最低分 from course left join score on course.cid = score.course_id group by score.course_id; 29、按各科平均成绩从低到高和及格率的百分数从高到低顺序; select course_id, avg(score) as avg_score, sum(case when score.score > 60 then 1 else 0 end) / count(1) * 100 as 及格率 from score group by course_id order by avg(score) desc, 及格率 asc; 30、课程平均分从高到低显示(显示任课老师); select course.cname, t1.avg_score, teacher.tname from course, teacher, ( select course_id, avg(score) as avg_score from score group by course_id order by avg_score desc ) as t1 where course.cid = t1.course_id and course.teacher_id = teacher.tid order by t1.avg_score desc; 31、查询各科成绩前三名的记录(不考虑成绩并列情况) select score.sid, score.student_id, score.course_id, score.sid, t1.first_score, t1.second_score, t1.third_score from score inner join ( select s1.sid, (select score from score as s2 where s1.course_id = s2.course_id order by score desc limit 0,1) as first_score, (select score from score as s3 where s1.course_id = s3.course_id order by score desc limit 1,1) as second_score, (select score from score as s4 where s1.course_id = s4.course_id order by score desc limit 2,1) as third_score from score as s1 ) as t1 on score.sid = t1.sid where score.score in ( t1.first_score, t1.second_score, t1.third_score ); 32、查询每门课程被选修的学生数; # 包含了没有被选修的课程显示0 select course.cid, ifnull(t1.count_students,0) as count_student from course left join ( select course_id, count(student_id) as count_students from score group by course_id ) as t1 on course.cid = t1.course_id; 33、查询选修了2门以上课程的全部学生的学号和姓名; select sid, sname from student where sid in ( select student_id from score group by student_id having count(course_id) > 2 ); 34、查询男生、女生的人数,按倒序排列; select gender, count(sid) as count_student from student group by gender order by count_student desc; 35、查询姓“张”的学生名单; select student.sid, student.sname, student.gender, class.caption from student inner join class on student.class_id = class.cid where student.sname like '张%'; 36、查询同名同姓学生名单,并统计同名人数; select sname, count(sname) as count_sname from student group by sname having count(sname) > 1; 37、查询每门课程的平均成绩,结果按平均成绩升序排列,平均成绩相同时,按课程号降序排列; select course_id, avg(score) as avg_score from score group by course_id order by avg_score, course_id desc; 38、查询课程名称为“数学”,且分数低于60的学生姓名和分数; select student.sname, t1.score from student inner join ( select score.student_id, score.score from score inner join course on score.course_id = course.cid where course.cname = '数学' and score.score < 60 ) as t1 on student.sid = t1.student_id; 39、查询课程编号为“3”且课程成绩在80分以上的学生的学号和姓名; select sid, sname from student where sid in ( select student_id from score where course_id = 3 and score > 80 ); 40、求选修了课程的学生人数 select course_id, count(student_id) as count_student from score group by course_id; 41、查询选修“王五”老师所授课程的学生中,成绩最高和最低的学生姓名及其成绩; # 教的课可能包含多门,按课程id来分的!包含了最高,最低成绩相等的情况 select student.sname, t2.course_id, t2.score, t2.max_score, t2.min_score from student inner join ( select score.student_id, score.course_id, score.score, t1.max_score, t1.min_score from score, ( select course_id, max(score) as max_score , min(score) as min_score from score where course_id in ( select cid from course inner join teacher on course.teacher_id = teacher.tid where teacher.tname = '王五' ) group by course_id ) as t1 where score.course_id = t1.course_id and score.score in ( max_score, min_score ) ) as t2 on student.sid = t2.student_id; 42、查询各个课程及相应的选修人数; # 包含了没有被选修的课程显示0 select course.cname, ifnull(t1.count_student,0) as count_student from course left join ( select course_id, count(student_id) as count_student from score group by course_id ) as t1 on course.cid = t1.course_id; 43、查询不同课程但成绩相同的学生的学号、课程号、学生成绩; # 不同的学生之间,成绩相同 这里有问题!! select distinct s1.student_id, s2.student_id, s1.course_id as s1_course_id, s2.course_id as s2_course_id, s1.score, s2.score from score as s1, score as s2 where s1.course_id != s2.course_id and s1.score = s2.score; select distinct # 同一个学生,成绩相同 s1.student_id, s2.student_id, s1.course_id as s1_course_id, s2.course_id as s2_course_id, s1.score, s2.score from score as s1, score as s2 where s1.student_id = s2.student_id and s1.course_id != s2.course_id and s1.score = s2.score; 44、查询每门课程成绩最好的前两名学生id和姓名; # 这个有排名 包括了成绩相同的! select c.sname, d.cname, a.score from score a inner join ( select course_id, score, rank from ( select a.course_id, a.score, count(*) as rank from (select course_id, score from score group by course_id, score order by course_id, score desc) a inner join (select course_id, score from score group by course_id, score order by course_id, score desc) b on a.course_id = b.course_id and a.score <= b.score group by course_id, score ) t1 where rank in (1, 2) order by course_id, rank ) b on a.course_id = b.course_id and a.score = b.score inner join student c on a.student_id = c.sid inner join course d on a.course_id = d.cid; 45、检索至少选修两门课程的学生学号; select student_id from score group by student_id having count(course_id) >= 2; 46、查询没有学生选修的课程的课程号和课程名; select cid, cname from course where cid not in ( select course_id from score group by course_id ); 47、查询没带过任何班级的老师id和姓名; select tid, tname from teacher where tid not in ( select tid from teach2cls group by tid ); 48、查询有两门以上课程超过80分的学生id及其平均成绩; select student_id, avg(score) as avg_score from score where student_id in ( select student_id from score where score > 80 group by student_id having count(course_id) > 2 ) group by student_id; 49、检索“3”课程分数小于60,按分数降序排列的同学学号; select student_id, score from score where course_id = 3 and score < 60 order by score desc; 50、删除编号为“2”的同学的“1”课程的成绩; delete from score where sid = ( select t1.sid from ( select sid from score where student_id = 2 and course_id = 1 ) as t1 ); 51、查询同时选修了物理课和生物课的学生id和姓名; select sid, sname from student where sid in ( select student_id from score where course_id in ( select cid from course where course.cname in ( '物理', '生物' ) ) group by student_id having count(course_id) = 2 );