ORM aggregate query and native database operation

1. Aggregate query

Classification is divided into whole table aggregation and grouping aggregation .

1.1 Whole table aggregation

First import from django.db.models import *
Aggregate functions Sum Avg Count Max Min

grammar ：
MyModel.objects.aggregate( Outcome variable = Aggregate functions （’ Column ‘）)
Return dictionary ：{ Result variable name ： value }

1.2 Group aggregation

Group first , Repolymerization

1.2.1 Group first

MyModel.objects.values(‘ Column 1’,’ Column 2‘)

1.2.2 use annotate polymerization

2. Native database operations

prevent sql Inject , Not recommended
raw return RawQuerySet Just cycle
Inquire about :

res = Book.objects.raw('select * from bookstore_book where id =%s'%(id))

2.1 The cursor

Operate the database completely across model classes , Check, modify and delete

2.1.1 Import cursor

from django.db import connection

2.1.2 establish cursor object

Usually use with sentence , Easy to release cursor resources

from django.db import connection
with connection.cusor() as cur:
	cur.exectue('SQL',' Splicing parameter ')