from django.db import models

class Employee(models.Model):

    name = models.CharField(max_length=16)

    age = models.IntegerField()

    salary = models.IntegerField()

    province = models.CharField(max_length=32)

    dept = models.CharField(max_length=16)

    def __str__(self):

        return self.name

    class Meta:

        db_table = "employee"

import os

if __name__ == '__main__':

    # 加载 Django 项目的配置信息

    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "mysite2.settings")

    # 导入 Django，并启动 Django 项目

    import django

    django.setup()

    from app04 import models

    from django.db.models import Avg

    # 计算每个部门的平均工资

    ret = models.Employee.objects.values("dept").annotate(avg=Avg("salary")).values("dept", "avg")

    print(ret)

from django.db import models

class Employee2(models.Model):

    name = models.CharField(max_length=16)

    age = models.IntegerField()

    salary = models.IntegerField()

    province = models.CharField(max_length=32)

    dept = models.ForeignKey(to="Dept")

    def __str__(self):

        return self.name

    class Meta:

        db_table = "employee2"

class Dept(models.Model):

    name = models.CharField(max_length=16, unique=True)

    def __str__(self):

        return self.name

    class Meta:

        db_table = "dept2"

import os

if __name__ == '__main__':

    # 加载 Django 项目的配置信息

    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "mysite2.settings")

    # 导入 Django，并启动 Django 项目

    import django

    django.setup()

    from app04 import models

    from django.db.models import Avg

    # 连表查询计算每个部门的平均工资

    ret = models.Employee2.objects.values("dept_id").annotate(avg=Avg("salary")).values("dept__name","avg")  # 一个双下划线表示跨一张表查询

    print(ret)