###########1 聚合查询(聚合函数:最大,最小,和,平均,总个数)
from django.db.models import Avg,Max,Min,Count,Sum #1 计算所有图书的平均价格 # aggregate结束,已经不是queryset对象了 # book=models.Book.objects.all().aggregate(Avg('price')) # 起别名 # book=models.Book.objects.all().aggregate(avg=Avg('price')) #2 计算总图书数 # book = models.Book.objects.all().aggregate(count=Count('id')) # 3 计算最低价格的图书 # book = models.Book.objects.all().aggregate(min=Min('price')) # 4 计算最大价格图书 # book = models.Book.objects.all().aggregate(max=Max('price')) # print(book)
2 分组查询
'''
查询每一个部门名称以及对应的员工数
book:
id name price publish
1 金品 11.2 1
2 西游 14.2 2
3 东游 16.2 2
4 北邮 19.2 3
''' # 示例一:查询每一个出版社id,以及出书平均价格 # select publish_id,avg(price) from app01_book group by publish_id; # annotate # annotate() 内写聚合函数 # values在前表示group by的字段 # values在后表示取某几个字段 # filter在前表示where # filter在后表示having # from django.db.models import Avg, Count, Max, Min # ret=models.Book.objects.values('publish_id').annotate(avg=Avg('price')).values('publish_id','avg') # print(ret) # 查询出版社id大于1的出版社id,以及出书平均价格 #select publish_id,avg(price) from app01_book where publish_id>1 group by publish_id; # ret=models.Book.objects.values('publish_id').filter(publish_id__gt=1).annotate(avg=Avg('price')).values('publish_id','avg') # print(ret) # 查询出版社id大于1的出版社id,以及出书平均价格大于30的 # select publish_id,avg(price)as aaa from app01_book where publish_id>1 group by publish_id HAVING aaa>30; # ret = models.Book.objects.values('publish_id').filter(publish_id__gt=1).annotate(avg=Avg('price')).filter(avg__gt=30).values( # 'publish_id', 'avg') # print(ret) ## 查询每一个出版社出版的书籍个数 # pk 代指主键 # ret=models.Book.objects.get(pk=1) # print(ret.name) # ret=models.Publish.objects.values('pk').annotate(count=Count('book__id')).values('name','count') # print(ret) # 如果没有指定group by的字段,默认就用基表(Publish)主键字段作为group by的字段 # ret=models.Publish.objects.annotate(count=Count('book__id')).values('name','count') # print(ret) # 另一种方式实现 # ret=models.Book.objects.values('publish').annotate(count=Count('id')).values('publish__name','count') # print(ret) #查询每个作者的名字,以及出版过书籍的最高价格(建议使用分组的表作为基表) # 如果不用分组的表作为基表,数据不完整可能会出现问题 # ret=models.Author.objects.values('pk').annotate(max=Max('book__price')).values('name','max') # ret = models.Author.objects.annotate(max=Max('book__price')).values('name', 'max') # ret= models.Book.objects.values('authors__id').annotate(max=Max('price')).values('authors__name','max') # print(ret) #查询每一个书籍的名称,以及对应的作者个数 # ret=models.Book.objects.values('pk').annotate(count=Count('authors__id')).values('name','count') # ret=models.Book.objects.annotate(count=Count('authors__id')).values('name','count') # ret=models.Author.objects.values('book__id').annotate(count=Count('id')).values('book__name','count') # # print(ret) #统计不止一个作者的图书 # ret=models.Book.objects.values('pk').annotate(count=Count('authors__id')).filter(count__gt=1).values('name','count') # ret = models.Author.objects.values('book__id').annotate(count=Count('id')).filter(count__gt=1).values('book__name', 'count') # print(ret) # 统计价格数大于10元,作者的图书 ret = models.Book.objects.values('pk').filter(price__gt=10).annotate(count=Count('authors__id')).values('name', 'count') print(ret) #统计价格数大于10元,作者个数大于1的图书 ret = models.Book.objects.values('pk').filter(price__gt=10).annotate(count=Count('authors__id')).filter(count__gt=1).values('name', 'count') print(ret)
标签:__,count,聚合,models,ret,查询,values,分组,id From: https://www.cnblogs.com/97zs/p/17868008.html