Django面試題系列(2)-ORM實現複雜查詢
阿新 • • 發佈:2019-01-24
假設有以下ORM
模型:
from django.db import models
class Student(models.Model):
"""學生表"""
name = models.CharField(max_length=100)
gender = models.SmallIntegerField()
class Meta:
db_table = 'student'
class Course(models.Model):
"""課程表"""
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):
"""分數表"""
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):
"""老師表"""
name = models.CharField(max_length=100)
class Meta:
db_table = 'teacher'
使用之前學到過的操作實現下面的查詢操作:
查詢平均成績大於60分的同學的id和平均成績;
查詢所有同學的id、姓名、選課的數量、總成績;
查詢姓“李”的老師的個數;
查詢沒學過“李老師”課的同學的id、姓名;
查詢學過課程id為1和2的所有同學的id、姓名;
查詢學過“黃老師”所教的“所有課”的同學的id、姓名;
查詢所有課程成績小於60分的同學的id和姓名;
查詢沒有學全所有課的同學的id、姓名;
查詢所有學生的姓名、平均分,並且按照平均分從高到低排序;
查詢各科成績的最高和最低分,以如下形式顯示:課程ID,課程名稱,最高分,最低分;
查詢沒門課程的平均成績,按照平均成績進行排序;
統計總共有多少女生,多少男生;
將“黃老師”的每一門課程都在原來的基礎之上加5分;
查詢兩門以上不及格的同學的id、姓名、以及不及格課程數;
查詢每門課的選課人數;
參考答案:
查詢平均成績大於60分的同學的id和平均成績;
rows = Student.objects.annotate(avg=Avg("score__number")).filter(avg__gte=60).values("id","avg") for row in rows: print(row)
查詢所有同學的id、姓名、選課的數、總成績;
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)
查詢姓“李”的老師的個數;
teacher_nums = Teacher.objects.filter(name__startswith="李").count() print(teacher_nums)
查詢沒學過“黃老師”課的同學的id、姓名;
rows = Student.objects.exclude(score__course__teacher__name="黃老師").values('id','name') for row in rows: print(row)
查詢學過id為1和2的所有同學的id、姓名;
rows = Student.objects.filter(score__course__in=[1,2]).distinct().values('id','name') for row in rows: print(row)
查詢學過“黃老師”所教的所有課的同學的學號、姓名;
rows = Student.objects.annotate(nums=Count("score__course",filter=Q(score__course__teacher__name='黃老師'))) .filter(nums=Course.objects.filter(teacher__name='黃老師').count()).values('id','name') for row in rows: print(row)
查詢所有課程成績小於60分的同學的id和姓名;
students = Student.objects.exclude(score__number__gt=60) for student in students: print(student)
查詢沒有學全所有課的同學的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)
查詢所有學生的姓名、平均分,並且按照平均分從高到低排序;
students = Student.objects.annotate(avg=Avg("score__number")).order_by("-avg").values('name','avg') for student in students: print(student)
查詢各科成績的最高和最低分,以如下形式顯示:課程ID,課程名稱,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)
查詢每門課程的平均成績,按照平均成績進行排序;
courses = Course.objects.annotate(avg=Avg("score__number")).order_by('avg').values('id','name','avg') for course in courses: print(course)
統計總共有多少女生,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)
將“黃老師”的每一門課程都在原來的基礎之上加5分;
rows = Score.objects.filter(course__teacher__name='黃老師').update(number=F("number")+5) print(rows)
查詢兩門以上不及格的同學的id、姓名、以及不及格課程數;
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)
查詢每門課的選課人數;
courses = Course.objects.annotate(student_nums=Count("score__student")).values('id','name','student_nums') for course in courses: print(course)