假设有以下ORM
模型:
from django.db import models
class Student(models.Model):
"""学生表"""
name = models.CharField(max_length=100)
gender = models.SmallIntegerField()
class Meta:
db_table = 'student'
class Course(models.Model):
"""课程表"""
name = models.CharField(max_length=100)
teacher = models.ForeignKey("Teacher",on_delete=models.SET_NULL,null=True)
class Meta:
db_table = 'course'
class Score(models.Model):
"""分数表"""
student = models.ForeignKey("Student",on_delete=models.CASCADE)
course = models.ForeignKey("Course",on_delete=models.CASCADE)
number = models.FloatField()
class Meta:
db_table = 'score'
class Teacher(models.Model):
"""老师表"""
name = models.CharField(max_length=100)
class Meta:
db_table = 'teacher'
使用之前学到过的操作实现下面的查询操作:
-
查询平均成绩大于60分的同学的id和平均成绩;
-
查询所有同学的id、姓名、选课的数量、总成绩;
-
查询姓“李”的老师的个数;
-
查询没学过“李老师”课的同学的id、姓名;
-
查询学过课程id为1和2的所有同学的id、姓名;
-
查询学过“黄老师”所教的“所有课”的同学的id、姓名;
-
查询所有课程成绩小于60分的同学的id和姓名;
-
查询没有学全所有课的同学的id、姓名;
-
查询所有学生的姓名、平均分,并且按照平均分从高到低排序;
-
查询各科成绩的最高和最低分,以如下形式显示:课程ID,课程名称,最高分,最低分;
-
查询没门课程的平均成绩,按照平均成绩进行排序;
-
统计总共有多少女生,多少男生;
-
将“黄老师”的每一门课程都在原来的基础之上加5分;
-
查询两门以上不及格的同学的id、姓名、以及不及格课程数;
-
查询每门课的选课人数;
参考答案:
-
查询平均成绩大于60分的同学的id和平均成绩;
rows = Student.objects.annotate(avg=Avg("score__number")).filter(avg__gte=60).values("id","avg") for row in rows: print(row)
-
查询所有同学的id、姓名、选课的数、总成绩;
rows = Student.objects.annotate(course_nums=Count("score__course"),total_score=Sum("score__number")) .values("id","name","course_nums","total_score") for row in rows: print(row)
-
查询姓“李”的老师的个数;
teacher_nums = Teacher.objects.filter(name__startswith="李").count() print(teacher_nums)
-
查询没学过“黄老师”课的同学的id、姓名;
rows = Student.objects.exclude(score__course__teacher__name="黄老师").values('id','name') for row in rows: print(row)
-
查询学过id为1和2的所有同学的id、姓名;
rows = Student.objects.filter(score__course__in=[1,2]).distinct().values('id','name') for row in rows: print(row)
-
查询学过“黄老师”所教的所有课的同学的学号、姓名;
rows = Student.objects.annotate(nums=Count("score__course",filter=Q(score__course__teacher__name='黄老师'))) .filter(nums=Course.objects.filter(teacher__name='黄老师').count()).values('id','name') for row in rows: print(row)
-
查询所有课程成绩小于60分的同学的id和姓名;
students = Student.objects.exclude(score__number__gt=60) for student in students: print(student)
-
查询没有学全所有课的同学的id、姓名;
students = Student.objects.annotate(num=Count(F("score__course"))).filter(num__lt=Course.objects.count()).values('id','name') for student in students: print(student)
-
查询所有学生的姓名、平均分,并且按照平均分从高到低排序;
students = Student.objects.annotate(avg=Avg("score__number")).order_by("-avg").values('name','avg') for student in students: print(student)
-
查询各科成绩的最高和最低分,以如下形式显示:课程ID,课程名称,最高分,最低分:
courses = Course.objects.annotate(min=Min("score__number"),max=Max("score__number")).values("id",'name','min','max') for course in courses: print(course)
-
查询每门课程的平均成绩,按照平均成绩进行排序;
courses = Course.objects.annotate(avg=Avg("score__number")).order_by('avg').values('id','name','avg') for course in courses: print(course)
-
统计总共有多少女生,多少男生;
rows = Student.objects.aggregate(male_num=Count("gender",filter=Q(gender=1)),female_num=Count("gender",filter=Q(gender=2))) print(rows)
-
将“黄老师”的每一门课程都在原来的基础之上加5分;
rows = Score.objects.filter(course__teacher__name='黄老师').update(number=F("number")+5) print(rows)
-
查询两门以上不及格的同学的id、姓名、以及不及格课程数;
students = Student.objects.annotate(bad_count=Count("score__number",filter=Q(score__number__lt=60))).filter(bad_count__gte=2).values('id','name','bad_count') for student in students: print(student)
-
查询每门课的选课人数;
courses = Course.objects.annotate(student_nums=Count("score__student")).values('id','name','student_nums') for course in courses: print(course)