如何使用Python跨 MySQL 表的列执行算术？

Python是一种动态语言， Python应用程序可以与数据库服务器集成。用于从Python访问 MySQL 数据库的模块是 MySQL Connector Python。 PyMySQL、MySQLDB 和 mysqlclient 是其他Python模块，用于在Python中与 MySQL 数据库服务器进行通信。但是，我们将在本文中使用 MySQL Connector Python ，因为它是一个完全用Python编写的 API，这意味着它没有依赖项，只需要标准库。

为了对列数据执行算术运算，MySQL 具有算术运算符。这些运算符可用于对数据执行计算。 MySQL中的算术运算符如下：

Operation	MySQL Arithmetic Operator	Syntax in MySQL
Addition	+	SELECT op1 + op2 FROM tablename;
Subtraction	–	SELECT op1 – op2 FROM tablename;
Division	/	SELECT op1 / op2 FROM tablename;
Multiplication	*	SELECT op1 * op2 FROM tablename;
Modulus	%	SELECT op1 % op2 FROM tablename;

在上表中， op1和op2可以是列名或数值（在这种情况下不需要“from”子句）。以下程序将帮助您更好地了解这些运算符的使用。

使用中的数据库：

我们将在我们的程序中使用产品信息表。它由产品名称、成本价、售价、税金和购买数量组成。

示例 1：加法运算符的使用

Python3

# Import required packages
import mysql.connector
  
# Establish connection to MySQL database
mydb = mysql.connector.connect(
  host = "localhost",
  user = "username",
  password = "geeksforgeeks",
  database = "grocery"
)
  
# MySQLCursorDict creates a cursor
# that returns rows as dictionaries
mycursor = mydb.cursor( dictionary = True )
  
# MySQL query for getting total
# sale amount (i.e. selling price + tax)
query = "SELECT Selling_price, \
                tax, \
                concat(Selling_price + tax) AS sale_amount \
         FROM product"
  
# Execute the query 
mycursor.execute( query )
# Fetch result of query
myresult = mycursor.fetchall()
  
# Print result of query
print(f"SP \t Tax \t Sale Amount")
  
for row in myresult:
    
      # Each value printed for display purpose (you can simply print row)
    print(f"{ row[ 'Selling_price' ]} \t { row[ 'tax' ]} \t { row[ 'sale_amount' ]}")
  
mydb.close()

输出：

示例 2：减法运算符的使用。

蟒蛇3

# Import required packages
import mysql.connector
  
# Establish connection to MySQL database
mydb = mysql.connector.connect(
  host = "localhost" ,
  user = "username" ,
  password = "geeksforgeeks" ,
  database = "grocery"
)
  
# MySQLCursorDict creates a cursor
# that returns rows as dictionaries
mycursor = mydb.cursor(dictionary = True )
  
# MySQL query for getting profit
# (i.e. selling price - cost price)
query = "SELECT selling_price, \
                cost_price, \
                concat(selling_price - cost_price) AS profit \
         FROM product_info"
  
# Execute the query 
mycursor.execute( query )
  
# Fetch result of query
myresult = mycursor.fetchall()
  
# Print result of query
print(f"SP \t CP \t Profit")
for row in myresult:
  print(f"{ row[ 'selling_price' ]} \t { row[ 'cost_price' ]} \t { row[ 'profit' ]}")
  
mydb.close()

输出：

示例 3：乘法运算符的使用

蟒蛇3

# Import required packages
import mysql.connector
  
# Establish connection to MySQL database
mydb = mysql.connector.connect(
  host = "localhost" ,
  user = "username" ,
  password = "geeksforgeeks" ,
  database = "grocery"
)
  
# MySQLCursorDict creates a cursor that returns rows as dictionaries
mycursor = mydb.cursor(dictionary = True)
  
# MySQL query for getting total amount (i.e. sale amount * quantity)
query = "SELECT selling_price, \
                tax, \
                concat((selling_price * tax)) AS total_amount \
         FROM product_info"
  
# Execute the query 
mycursor.execute( query )
  
# Fetch result of query
myresult = mycursor.fetchall()
  
# Print result of query
print(f"SP \t Tax \t Total")
for row in myresult:
  print(f"{row[ 'selling_price' ]} \t { row[ 'tax' ]}\t{row['total_amount']}")
  
# Close database connection
mydb.close()

输出：

示例 4：除法运算符的使用。

蟒蛇3

# Import required packages
import mysql.connector
  
# Establish connection to MySQL database
mydb = mysql.connector.connect(
  host = "localhost" ,
  user = "username" ,
  password = "geeksforgeeks" ,
  database = "grocery"
)
  
# MySQLCursorDict creates a cursor
# that returns rows as dictionaries
mycursor = mydb.cursor( dictionary = True )
  
# MySQL query for getting halved selling price of all products
query = "SELECT selling_price, \
                concat(selling_price / 2) AS discount_price \
         FROM product_info"
  
# Execute the query 
mycursor.execute( query )
  
# Fetch result of query
myresult = mycursor.fetchall()
  
# Print result of query
print(f"SP \t Discounted Price")
for row in myresult:
  print(f"{ row[ 'selling_price' ]} \t { row ['discount_price']}")
  
# Close database connection
mydb.close()

输出：

示例 5：模数运算符的使用。

蟒蛇3

# Import required packages
import mysql.connector
  
# Establish connection to MySQL database
mydb = mysql.connector.connect(
  host = "localhost" ,
  user = "username" ,
  password = "geeksforgeeks" ,
  database = "grocery"
)
  
# MySQLCursorDict creates a cursor
# that returns rows as dictionaries
mycursor = mydb.cursor(dictionary = True)
  
# MySQL query for getting remainder
query = "SELECT selling_price, \
                cost_price, \
                concat(selling_price % cost_price) AS mod_example \
         FROM product_info"
  
# Execute the query 
mycursor.execute( query )
  
# Fetch result of query
myresult = mycursor.fetchall()
  
# Print result of query
print(f"SP \t Qnty \t MOD")
for row in myresult:
  print(f"{ row [ 'selling_price' ]}
              \t { row [ 'cost_price' ]}
                  \t{row[ 'mod_example' ]}")
  
# Close database connection
mydb.close()

输出：