Django:此数据库后端不支持不同的ON字段

如何修复django中此数据库后端不支持的字段上的DISTINCT?

total = grade.objects.values('Grading_Categories').annotate(Average= Avg('Average')).filter(Teacher = m.id).distinct('Grading_Categories')

这是我的模型.py

class finalrating(models.Model):
    Teacher = models.ForeignKey(EmployeeUser, related_name='+', on_delete=models.CASCADE,
                                null=True, blank=True)
    Subjects = models.ForeignKey(Subject, related_name='+', on_delete=models.CASCADE, null=True)
    Students_Enrollment_Records = models.ForeignKey(StudentsEnrolledSubject, related_name='+',
                                                    on_delete=models.CASCADE, null=True)
    Average = models.FloatField(null=True, blank=True)
    Status = models.CharField(max_length=500, null=True, choices=Pending_Request, blank=True)

我的问题出在这条线上