1 2、查询“生物”课程比“物理”课程成绩高的所有学生的学号；2 思路：3 获取所有有生物课程的人(学号，成绩) -临时表4 获取所有有物理课程的人(学号，成绩) -临时表5 根据【学号】连接两个临时表：6 学号 物理成绩 生物成绩7

8 然后再进行筛选9

10 select A.student_id,sw,ty from

11

12 (select student_id,num as sw from score left join course on score.course_id = course.cid where course.cname = '生物') as A13

14 left join15

16 (select student_id,num as ty from score left join course on score.course_id = course.cid where course.cname = '体育') as B17

18 on A.student_id = B.student_id where sw > if(isnull(ty),0,ty);19

20 3、查询平均成绩大于60分的同学的学号和平均成绩；21 思路：22 根据学生分组，使用avg获取平均值，通过having对avg进行筛选23

24 select student_id,avg(num) from score group by student_id having avg(num) > 60

25

26 4、查询所有同学的学号、姓名、选课数、总成绩；27

28 select score.student_id,sum(score.num),count(score.student_id),student.sname29 from

30 score left join student on score.student_id =student.sid31 group by score.student_id32

33 5、查询姓“李”的老师的个数；34 select count(tid) from teacher where tname like '李%'

35

36 select count(1) from (select tid from teacher where tname like '李%') as B37

38 6、查询没学过“叶平”老师课的同学的学号、姓名；39 思路：40 先查到“李平老师”老师教的所有课ID41 获取选过课的所有学生ID42 学生表中筛选43 select * from student where sid not in(44 select DISTINCT student_id from score where score.course_id in(45 select cid from course left join teacher on course.teacher_id = teacher.tid where tname = '李平老师'

46 )47 )48

49 7、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；50 思路：51 先查到既选择001又选择002课程的所有同学52 根据学生进行分组，如果学生数量等于2表示，两门均已选择53

54 select student_id,sname from

55

56 (select student_id,course_id from score where course_id = 1 or course_id = 2) as B57

58 left join student on B.student_id = student.sid group by student_id HAVING count(student_id) > 1

59

60

61 8、查询学过“叶平”老师所教的所有课的同学的学号、姓名；62

63 同上，只不过将001和002变成 in(叶平老师的所有课)64

65 9、查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名；66 同第1题67

68

69 10、查询有课程成绩小于60分的同学的学号、姓名；70

71 select sid,sname from student where sid in(72 select distinct student_id from score where num < 60

73 )74

75 11、查询没有学全所有课的同学的学号、姓名；76 思路：77 在分数表中根据学生进行分组，获取每一个学生选课数量78 如果数量 ==总课程数量，表示已经选择了所有课程79

80 select student_id,sname81 from score left join student on score.student_id =student.sid82 group by student_id HAVING count(course_id) = (select count(1) fromcourse)83

84

85 12、查询至少有一门课与学号为“001”的同学所学相同的同学的学号和姓名；86 思路：87 获取 001同学选择的所有课程88 获取课程在其中的所有人以及所有课程89 根据学生筛选，获取所有学生信息90 再与学生表连接，获取姓名91

92 select student_id,sname, count(course_id)93 from score left join student on score.student_id =student.sid94 where student_id != 1 and course_id in (select course_id from score where student_id = 1) group by student_id95

96 13、查询至少学过学号为“001”同学所有课的其他同学学号和姓名；97 先找到和001的学过的所有人98 然后个数 ＝ 001所有学科 ＝＝》 其他人可能选择的更多99

100 select student_id,sname, count(course_id)101 from score left join student on score.student_id =student.sid102 where student_id != 1 and course_id in (select course_id from score where student_id = 1) group by student_id having count(course_id) ＝ (select count(course_id) from score where student_id = 1)103

104 14、查询和“002”号的同学学习的课程完全相同的其他同学学号和姓名；105

106 个数相同107 002学过的也学过108

109 select student_id,sname from score left join student on score.student_id = student.sid where student_id in(110 select student_id from score where student_id != 1 group by student_id HAVING count(course_id) = (select count(1) from score where student_id = 1)111 ) and course_id in (select course_id from score where student_id = 1) group by student_id HAVING count(course_id) = (select count(1) from score where student_id = 1)112

113

114 15、删除学习“叶平”老师课的score表记录；115

116 delete from score where course_id in(117 select cid from course left join teacher on course.teacher_id = teacher.tid where teacher.name = '叶平'

118 )119

120 16、向SC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“002”课程的同学学号；②插入“002”号课程的平均成绩；121 思路：122 由于insert 支持123 inset into tb1(xx,xx) select x1,x2 fromtb2;124 所有，获取所有没上过002课的所有人，获取002的平均成绩125

126 insert into score(student_id, course_id, num) select sid,2,(select avg(num) from score where course_id = 2)127 from student where sid not in(128 select student_id from score where course_id = 2

129 )130

131 17、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；132 select sc.student_id,133 (select num from score left join course on score.course_id = course.cid where course.cname = "生物" and score.student_id=sc.student_id) as sy,134 (select num from score left join course on score.course_id = course.cid where course.cname = "物理" and score.student_id=sc.student_id) as wl,135 (select num from score left join course on score.course_id = course.cid where course.cname = "体育" and score.student_id=sc.student_id) as ty,136 count(sc.course_id),137 avg(sc.num)138 fromscore as sc139 group by student_id desc140

141 18、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；142

143 select course_id, max(num) as max_num, min(num) as min_num fromscore group by course_id;144

145 19、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；146 思路：case when .. then147 select course_id, avg(num) as avgnum,sum(case when score.num > 60 then 1 else 0 END)/count(1)*100 as percent fromscore group by course_id order by avgnum asc,percent desc;148

149 20、课程平均分从高到低显示(现实任课老师)；150

151 select avg(if(isnull(score.num),0,score.num)),teacher.tname fromcourse152 left join score on course.cid =score.course_id153 left join teacher on course.teacher_id =teacher.tid154

155 group by score.course_id156

157

158 21、查询各科成绩前三名的记录:(不考虑成绩并列情况)159 select score.sid,score.course_id,score.num,T.first_num,T.second_num fromscore left join160 (161 select162 sid,163 (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 0,1) as first_num,164 (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 3,1) as second_num165 from

166 score as s1167 ) as T168 on score.sid =T.sid169 where score.num <= T.first_num and score.num >=T.second_num170

171 22、查询每门课程被选修的学生数；172

173 select course_id, count(1) fromscore group by course_id;174

175 23、查询出只选修了一门课程的全部学生的学号和姓名；176 select student.sid, student.sname, count(1) fromscore177

178 left join student on score.student_id =student.sid179

180 group by course_id having count(1) = 1

181

182

183 24、查询男生、女生的人数；184 select * from

185 (select count(1) as man from student where gender='男') as A ,186 (select count(1) as feman from student where gender='女') as B187

188 25、查询姓“张”的学生名单；189 select sname from student where sname like '张%';190

191 26、查询同名同姓学生名单，并统计同名人数；192

193 select sname,count(1) as count fromstudent group by sname;194

195 27、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；196 select course_id,avg(if(isnull(num), 0 ,num)) as avg fromscore group by course_id order by avg asc,course_id desc;197

198 28、查询平均成绩大于85的所有学生的学号、姓名和平均成绩；199

200 select student_id,sname, avg(if(isnull(num), 0 ,num)) from score left join student on score.student_id =student.sid group by student_id;201

202 29、查询课程名称为“数学”，且分数低于60的学生姓名和分数；203

204 select student.sname,score.num fromscore205 left join course on score.course_id =course.cid206 left join student on score.student_id =student.sid207 where score.num < 60 and course.cname = '生物'

208

209 30、查询课程编号为003且课程成绩在80分以上的学生的学号和姓名；210 select * from score where score.student_id = 3 and score.num > 80

211

212 31、求选了课程的学生人数213

214 select count(distinct student_id) fromscore215

216 select count(c) from(217 select count(student_id) as c fromscore group by student_id) as A218

219 32、查询选修“杨艳”老师所授课程的学生中，成绩最高的学生姓名及其成绩；220

221 select sname,num fromscore222 left join student on score.student_id =student.sid223 where score.course_id in (select course.cid from course left join teacher on course.teacher_id = teacher.tid where tname='张磊老师') order by num desc limit 1;224

225 33、查询各个课程及相应的选修人数；226 select course.cname,count(1) fromscore227 left join course on score.course_id =course.cid228 group by course_id;229

230

231 34、查询不同课程但成绩相同的学生的学号、课程号、学生成绩；232 select DISTINCT s1.course_id,s2.course_id,s1.num,s2.num from score as s1, score as s2 where s1.num = s2.num and s1.course_id !=s2.course_id;233

234 35、查询每门课程成绩最好的前两名；235

236 select score.sid,score.course_id,score.num,T.first_num,T.second_num fromscore left join237 (238 select239 sid,240 (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 0,1) as first_num,241 (select num from score as s2 where s2.course_id = s1.course_id order by num desc limit 1,1) as second_num242 from

243 score as s1244 ) as T245 on score.sid =T.sid246 where score.num <= T.first_num and score.num >=T.second_num247

248 36、检索至少选修两门课程的学生学号；249 select student_id from score group by student_id having count(student_id) > 1

250

251 37、查询全部学生都选修的课程的课程号和课程名；252 select course_id,count(1) from score group by course_id having count(1) = (select count(1) fromstudent);253

254 38、查询没学过“叶平”老师讲授的任一门课程的学生姓名；255 select student_id,student.sname fromscore256 left join student on score.student_id =student.sid257 where score.course_id not in(258 select cid from course left join teacher on course.teacher_id = teacher.tid where tname = '张磊老师'

259 )260 group by student_id261

262 39、查询两门以上不及格课程的同学的学号及其平均成绩；263

264 select student_id,count(1) from score where num < 60 group by student_id having count(1) > 2

265

266 40、检索“004”课程分数小于60，按分数降序排列的同学学号；267 select student_id from score where num< 60 and course_id = 4order by num desc;268

269 41、删除“002”同学的“001”课程的成绩；270 delete from score where course_id = 1 and student_id = 2