#一 model表:
from django.db import models # Create your models here. class Teacher(models.Model): tid=models.AutoField(primary_key=True) tname=models.CharField(max_length=32) classes=models.ManyToManyField("Klass") def __str__(self): return self.tname class Meta: db_table ="teacher" class Grade(models.Model): gid=models.AutoField(primary_key=True) gname=models.CharField(max_length=32) def __str__(self): return self.gname class Meta: db_table ="grade" class Klass(models.Model): kid=models.AutoField(primary_key=True) kname=models.CharField(max_length=32) grade=models.ForeignKey("Grade",on_delete=models.CASCADE) def __str__(self): return self.kname class Meta: db_table ="klass" class Student(models.Model): sid=models.AutoField(primary_key=True) sname=models.CharField(max_length=32) gender=models.IntegerField(choices=((0,"男"),(1,"女"))) cls=models.ForeignKey("Klass",on_delete=models.CASCADE) def __str__(self): return self.sname class Meta: db_table ="student" class Course(models.Model): cid=models.AutoField(primary_key=True) cname=models.CharField(max_length=32) teacher=models.ForeignKey("Teacher",on_delete=models.CASCADE) def __str__(self): return self.cname class Meta: db_table = "course" class Score(models.Model): sid=models.AutoField(primary_key=True) student=models.ForeignKey("Student",on_delete=models.CASCADE) course=models.ForeignKey("Course",on_delete=models.CASCADE) score=models.IntegerField() def __str__(self): return str(self.student)+str(self.course)+str(self.score) class Meta: db_table ="score" # class Meta: # unique_together = (("student","course"),)
二.ER图
三.查询练习题
from django.shortcuts import render,HttpResponse # Create your views here. from django.db.models import Count,Avg,Min,Max,F,Q from .models import * def query(request): ''' 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,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、查询教过课程超过2门的老师的id和姓名; 12、查询学过编号“1”课程和编号“2”课程的同学的学号、姓名; 13、查询所带班级数最多的老师id和姓名; 14、查询有课程成绩小于60分的同学的学号、姓名; 15、查询男生、女生的人数,按倒序排列; 16、查询各个课程及相应的选修人数; 17、查询同时选修了物理课和生物课的学生id和姓名; 18、检索“3”课程分数小于60,按分数降序排列的同学学号; 19、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; 20、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; ''' #2、 查询学生总人数; # select count(*) from student res = Student.objects.all().aggregate(c=Count("sid")) print("res",res) # res {'c': 3} # #3、 查询“生物”课程和“物理”课程成绩都及格的学生id和姓名;(course表,score表,student表) # queryset = Student.objects.filter(score__course__cname="生物").filter(score__score__gt=60).values("sid","sname","score__score").distinct() # queryset2 = Student.objects.filter(score__course__cname="物理").filter(score__score__gt=60).values("sid","sname","score__score").distinct() queryset3=Score.objects.filter(score__gt=60).filter(course__cname="生物").values('student__sname','student__sid',"score","course__cname") queryset4=Score.objects.filter(score__gt=60).filter(course__cname="物理").values('student__sname','student__sid',"score","course__cname") # lst1 = [{'student__sname': '乔丹', 'student__sid': 1, 'score': 67, 'course__cname': '生物'}] # lst2 = [{'student__sname': '乔丹', 'student__sid': 1, 'score': 77, 'course__cname': '物理'}, # {'student__sname': '艾弗森', 'student__sid': 2, 'score': 88, 'course__cname': '物理'}] li1 = [] for dic in queryset3: li1.append({dic["student__sname"]: dic["student__sid"]}) li2 = [] for dic2 in queryset4: li2.append({dic["student__sname"]: dic["student__sid"]}) li3 = [] for name in li1: if name in li2: li3.append(name) print(li3) queryset5 = Score.objects.filter(score__gte=60,course__cname__in=["生物","物理"]).values('student__sname','student__sid',"score","course__cname") #老师的,不对 # print("queryset",queryset) # print("queryset2",queryset2) # print("queryset3",queryset3) # print("queryset4",queryset4) print("queryset5",queryset5) print() #4、 查询每个年级的班级数,取出班级数最多的前三个年级; q1 =Grade.objects.all().annotate(c=Count("klass")).values("gname","c").order_by('-c')[0:3] print("q1",q1) #5、 查询平均成绩最高的学生的id和姓名以及平均成绩; q5 =Student.objects.annotate(avg_score=Avg("score__score")).values('sname','avg_score').order_by("-avg_score")[0] print("q5",q5) #6、 查询每个年级的学生人数; q6= Grade.objects.annotate(c=Count("klass__student")).values("gname","c") print(q6) #7、 查询每位学生的学号,姓名,平均成绩; # q7 =Student.objects.annotate(avg_score=Avg("score__socre")).values("sid","sname","avg_score") #错误的写法 q7 =Student.objects.values("sid", "sname").annotate(avg_score=Avg("score__score")) print("q7",q7) #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及分数; # q8 =Student.objects.filter(sid=2).first().score_set.all().order_by("-score")[0] # 自己的思路? q8 = Student.objects.filter(sid=2).order_by("-score__score").values("sname","score__score","score__course__cname")[0] print("q8",q8) #9查询每一个姓“李”的老师所带班级数 q9=Teacher.objects.filter(tname__startswith="李").annotate(c=Count("classes")).values("tname","c") print(q9) #10、查询班级数小于5的年级id和年级名; q10=Grade.objects.annotate(c=Count("klass")).filter(c__lt=5).values("gid","gname") print(q10) #11、查询教过课程超过2门的老师的id和姓名; q11=Teacher.objects.annotate(c=Count("course")).filter(c__gt=2).values("tname","tid","c") print("q11",q11) #12、查询学过编号“1”课程和编号“2”课程的同学的学号、姓名; # q12=Student.objects.filter( Q(score__course__cid=1)&Q(score__course__cid=2)).values("sid","sname") # 自己想的,? ret = Student.objects.filter(score__course__cid=1).filter(score__course__cid=2).values("pk", "sname") # print("q12",q12) print(ret) #13、查询所带班级数最多的老师id和姓名; q13=Teacher.objects.annotate(c=Count("classes")).order_by('-c').values("tname","tid","c")[0] print(q13) # 14 查询有课程成绩小于60分的同学的学号、姓名; q14 =Student.objects.filter(score__score__lt=60).values("sid","sname","score__score").distinct() print(q14) #15、查询男生、女生的人数,按倒序排列; ? # q15_1 = Student.objects.filter(gender=0).count() # q15_2=Student.objects.filter(gender=1).count() # print("男",q15_1) # print("女",q15_2) q15 = Student.objects.values("gender").annotate(c=Count(1)).order_by("-c") #??? print(q15) #16、查询各个课程及相应的选修人数; q16 = Course.objects.annotate(c=Count("score__student__id")).values("cname","c") #可以 ret = Score.objects.values("course").annotate(c=Count(1)).values("course__cname", "c") # ??? print("ret",ret) print("q16",q16) #17、查询同时选修了物理课和生物课的学生id和姓名; q17=Student.objects.filter(score__course__cname="物理").filter(score__course__cname="生物").values("sid","sname") print("q17",q17) ret = Student.objects.filter(score__course__cname__in=["物理", "生物"]).values("pk", "sname").distinct()#??? in 不是同时满足吧 print("ret",ret) #18、检索“3”课程分数小于60,按分数降序排列的同学学号; q18=Course.objects.filter(cid=3).filter(score__score__lt=60).order_by("-score__score").values("score__student_id","score__student__sname") ret=Score.objects.filter(course_id=3, score__lt=60).order_by("-score").values("student_id") print("q18",q18) print(ret) #19、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; q19=Course.objects.annotate(avg_score=Avg("score__score")).order_by("avg_score").order_by("-cid").values("cname","avg_score")#错误,不能分开排序 q19=Course.objects.annotate(avg_score=Avg("score__score")).order_by("avg_score","-cid").values("cname","avg_score")# 正确 print("q19",q19) ret = Score.objects.values("course").annotate(avg_score=Avg("score")).order_by("avg_score", "-course")# 正确 print(ret) #20、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; q20=Course.objects.annotate(M_score=Max("score__score"),m_score=Min("score__score")).values("cid","M_score","m_score") print(q20) return HttpResponse("OK")