Peewee 简明教程
Peewee - Counting and Aggregation
我们可以通过附加 count() 方法来查找任何 SELECT 查询中报告的记录数。例如，以下语句返回 Contacts 表中 City=’Nasik’ 的行数。
We can find number of records reported in any SELECT query by attaching count() method. For example, following statement returns number of rows in Contacts table with City=’Nasik’.
qry=Contacts.select().where (Contacts.City=='Nasik').count()
print (qry)Example
SQL在 SELECT 查询中具有 GROUP BY 子句。Peewee 以 group_by() 方法的形式支持它。以下代码返回 Contacts 表中按城市统计的名称。
SQL has GROUP BY clause in SELECT query. Peewee supports it in the form of group_by() method. Following code returns city wise count of names in Contacts table.
from peewee import *
db = SqliteDatabase('mydatabase.db')
class Contacts(BaseModel):
RollNo = IntegerField()
Name = TextField()
City = TextField()
class Meta:
database = db
db.create_tables([Contacts])
qry=Contacts.select(Contacts.City, fn.Count(Contacts.City).alias('count')).group_by(Contacts.City)
print (qry.sql())
for q in qry:
print (q.City, q.count)Peewee 发出的 SELECT 查询将如下所示：
The SELECT query emitted by Peewee will be as follows −
('SELECT "t1"."City", Count("t1"."City") AS "count" FROM "contacts" AS "t1" GROUP BY "t1"."City"', [])