在QuerySet的聚合查詢中經常用到aggregate()和annotate()函式，但是這兩者有什麼區別呢？

 aggregate()是用於屬於QuerySet整個物件的彙總值，例如計算下列Student模型的平均年齡

class Student(models.Model):
    name = models.CharField(max_length=10)
    age = models.IntegerField()

    height = model.FloatField()

所需命令是

student_avg_age = Student.objects.all().aggregate(Avg('age'))
 

dict = Student.objects.aggregate(Avg(age), Max(height))

以老師和學生的模型為例，存在多對多關係

class Teacher(models.Model):
    name = models.CharField(max_length=100)
    age = models.IntegerField()
    student = models.ManyToManyField(Student)
 

t = Student.objects.annotate(Count('Teacher'))