如何使用pymysql和psycopg2执行SQL语句

news2024/12/26 21:57:45

在Python中，pymysql和psycopg2是两个非常流行的库，用于与MySQL和PostgreSQL数据库进行交互。本文将详细介绍如何使用这两个库来执行SQL查询、插入、更新和删除操作。
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1. 准备工作

首先，确保已经安装了pymysql和psycopg2库。如果尚未安装，可以通过以下命令安装：

pip install pymysql psycopg2

2. 连接数据库

2.1 连接MySQL

使用pymysql连接MySQL的代码示例：

import pymysql

# 连接数据库
connection = pymysql.connect(
    host='localhost',
    user='your_username',
    password='your_password',
    database='your_database',
    charset='utf8mb4',
    cursorclass=pymysql.cursors.DictCursor
)

# 创建游标对象
with connection.cursor() as cursor:
    # 执行SQL语句
    sql = "SELECT * FROM your_table"
    cursor.execute(sql)
    result = cursor.fetchall()
    for row in result:
        print(row)

# 关闭连接
connection.close()

2.2 连接PostgreSQL

使用psycopg2连接PostgreSQL的代码示例：

import psycopg2

# 连接数据库
connection = psycopg2.connect(
    host="localhost",
    user="your_username",
    password="your_password",
    dbname="your_database"
)

# 创建游标对象
with connection.cursor() as cursor:
    # 执行SQL语句
    sql = "SELECT * FROM your_table"
    cursor.execute(sql)
    result = cursor.fetchall()
    for row in result:
        print(row)

# 关闭连接
connection.close()

3. 执行SQL操作

3.1 查询操作

3.1.1 MySQL查询

with connection.cursor() as cursor:
    sql = "SELECT * FROM your_table WHERE condition"
    cursor.execute(sql)
    result = cursor.fetchall()
    for row in result:
        print(row)

3.1.2 PostgreSQL查询

with connection.cursor() as cursor:
    sql = "SELECT * FROM your_table WHERE condition"
    cursor.execute(sql)
    result = cursor.fetchall()
    for row in result:
        print(row)

3.2 插入操作

3.2.1 MySQL插入

with connection.cursor() as cursor:
    sql = "INSERT INTO your_table (column1, column2) VALUES (%s, %s)"
    cursor.execute(sql, ('value1', 'value2'))
    connection.commit()

3.2.2 PostgreSQL插入

with connection.cursor() as cursor:
    sql = "INSERT INTO your_table (column1, column2) VALUES (%s, %s)"
    cursor.execute(sql, ('value1', 'value2'))
    connection.commit()

3.3 更新操作

3.3.1 MySQL更新

with connection.cursor() as cursor:
    sql = "UPDATE your_table SET column1 = %s WHERE condition"
    cursor.execute(sql, ('new_value',))
    connection.commit()

3.3.2 PostgreSQL更新

with connection.cursor() as cursor:
    sql = "UPDATE your_table SET column1 = %s WHERE condition"
    cursor.execute(sql, ('new_value',))
    connection.commit()

3.4 删除操作

3.4.1 MySQL删除

with connection.cursor() as cursor:
    sql = "DELETE FROM your_table WHERE condition"
    cursor.execute(sql)
    connection.commit()

3.4.2 PostgreSQL删除

with connection.cursor() as cursor:
    sql = "DELETE FROM your_table WHERE condition"
    cursor.execute(sql)
    connection.commit()

4. 错误处理

在执行数据库操作时，可能会遇到各种错误，如连接失败、SQL语法错误等。正确的错误处理可以确保程序的健壮性。

try:
    with connection.cursor() as cursor:
        cursor.execute(sql)
except pymysql.MySQLError as e:
    print(f"Error: {e}")
finally:
    connection.close()