在Python中使用 SQLite 聚合函数

在本文中，我们将了解如何在 SQLite Python中使用聚合函数。聚合函数是一种数据库管理函数，它将许多行的值组合成一个汇总值。 Average（即算术平均值）、sum、max、min、Count 是常用的聚合函数。 SQLite 为我们提供了许多用于统计分析的聚合函数。

用于演示的数据库：要下载数据库，请单击此处。

最大（）函数

max()函数返回我们指定的列中所有值的最大值。

Syntax: max(name_of_the_column)

Python3

# import the sqlite module
import sqlite3
  
# establishing a connection to the database
connection = sqlite3.connect("sales.db")
  
# Obtain a cursor object
cursor = connection.cursor()
  
# Find the maximum yearly_sale
max_sale = "select max(yearly_sale) from sales1"
  
cursor.execute(max_sale)
  
print("The maximum yearly sale is is:")
print(cursor.fetchone()[0])
  
# Closing database connection
connection.close()

输出：

The maximum yearly sale is is:
98787.0

Min()函数

min()函数返回我们指定的列中所有值的最小值。

Syntax: min(name_of_the_column)

Python3

# import the sqlite module
import sqlite3
  
# establishing a connection to the database
connection   = sqlite3.connect("sales.db")
  
# Obtain a cursor object
cursor = connection.cursor()
  
# minimum yearly sale
min_sale = "select min(yearly_sale) from sales1"
  
cursor.execute(min_sale)
  
# Print the minimum score
print("The minimum yearly sale is:")
  
# fetching the result
print(cursor.fetchone()[0])
  
# Closing database connection
connection.close()

输出：

The minimum yearly sale is:
25659.0

平均（）函数

avg()函数返回我们指定的列中所有值的平均值或算术平均值。如果列中存在任何空值，则将其排除在外。

Syntax: avg(name_of_the_column)

Python3

# import the sqlite module
import sqlite3
  
# establishing a connection to the database
connection   = sqlite3.connect("sales.db")
  
# creating a cursor object
cursor = connection.cursor()
  
# average value of yearly_sales
avg_sale  = "select avg(yearly_sale) from sales1"
  
cursor.execute(avg_sale)
  
print("The average yearly sales is:")
  
print(cursor.fetchone())
# Closing database connection
connection.close()

输出：

The average yearly sales is:
(66441.75,)

总计（）函数

total()函数返回列的所有值的总和或总和。

Syntax: total(name_of_the_column)

Python3

# import the sqlite module
import sqlite3
  
# establishing a connection to the database
connection   = sqlite3.connect("sales.db")
  
# creating a cursor object
cursor = connection.cursor()
  
# total monthly_sale
Total_mon_sale= "select total(monthly_sale) from sales1"
cursor.execute(Total_mon_sale)
  
# Print the total score
print("The total monthly sale of all items is:")
  
print(cursor.fetchone()[0])
  
# Closing database connection
connection.close()

输出：

The total monthly sale of all items is:
26230.0

Sum()函数

sum()函数返回列的所有值的总和，如果所有值都为 null ，则返回 null。所以，total()函数是一个比较好的函数。

Syntax: sum(name_of_the_column)

Python3

# import the sqlite module
import sqlite3
  
# establishing a connection to the database
connection   = sqlite3.connect("sales.db")
  
# creating a cursor object
cursor = connection.cursor()
  
# sum of all the yearly sale
sum_yearly_sale = "select sum(yearly_sale) from sales1"
  
cursor.execute(sum_yearly_sale)
  
# Print the sum of scores
print("The sum of yearly sale is :")
  
print(cursor.fetchone()[0])
  
# Closing database connection
connection.close()

输出：

The sum of yearly sale is :
265767.0

计数（）函数

count()函数返回特定列或整个表中非空值的数量。

count of all rows in a table:

count(*)

count of all rows in a specified column:

count(name_of_the_column)

Python3

# import the sqlite module
import sqlite3
  
# establishing a connection to the database
connection   = sqlite3.connect("sales.db")
  
# creating a cursor object
cursor = connection.cursor()
  
# count of all the rows of the database
count = "select count(*) from sales1"
  
cursor.execute(count)
  
print("The count of all rows of the table  :")
print(cursor.fetchone()[0])
  
# Closing database connection
connection.close()

输出：

The count of all rows of the table  :
4