【转】python 借助pymysql操作MySQL及占位符问题

原文链接： python 借助pymysql操作MySQL及占位符问题

在python3中，主要借助pymysql进行MySQL操作，简单记录下基本的操作步骤：
操作流程一般分为3步：

1. 建立数据库连接
2. 执行操作（查询、插入、更新、删除等）
3. 关闭连接

代码

import pymysql


# 数据库连接
def connect():
    conn = pymysql.connect(host='localhost',
                           port=3306,
                           user='root',
                           password='root',
                           database='root',
                           charset='utf8')

    # 获取操作游标
    cursor = conn.cursor()
    return {"conn": conn, "cursor": cursor}

在执行操作时，借助游标方法： cursor.execute() 执行SQL操作。

# 1、查询操作并打印结果
def select_sql(table):
    connection = connect()
    conn, cursor = connection['conn'], connection['cursor']
    sql = "select * from %s" % table
    try:
        cursor.execute(sql)
        results = cursor.fetchall()
        print(results)
    except Exception as e:
        raise e
    finally:
        cursor.close()
        conn.close()


# 插入操作
def insert_sql(persons_values):
    connection = connect()
    conn, cursor = connection['conn'], connection['cursor']

    keys = ", ".join(persons_values.keys())
    qmark = ", ".join(["%s"] * len(persons_values))
    sql_insert = "insert into persons(%s) values (%s)" % (keys, qmark)
    print(sql_insert)
    try:
        cursor.execute(sql_insert, list(persons_values.values()))
        conn.commit()
        print("插入成功")
    except Exception as e:
        print(e)
        conn.rollback()
        print("插入失败")
    finally:
        cursor.close()
        conn.close()


# 利用字典进行插入
def insert_sql2(message):
    connection = connect()
    conn, cursor = connection['conn'], connection['cursor']

    sql_insert = "insert into persons(ID, LastName, FirstName) " \
                 "values (%(ID)s, %(LastName)s, %(FirstName)s)"
    try:
        cursor.execute(sql_insert, message)
        conn.commit()
        print("插入成功")
    except Exception as e:
        print(e)
        conn.rollback()
        print("插入失败")
    finally:
        cursor.close()
        conn.close()


# 更新数据库
def update_sql():
    connection = connect()
    conn, cursor = connection['conn'], connection['cursor']

    sql_update = "update persons set birthday=%s where ID=%s"
    try:
        cursor.execute(sql_update, ('2001/7/5', 3))
        conn.commit()
        print('更新成功')
    except Exception as e:
        print('更新失败', e)
        conn.rollback()
    finally:
        cursor.close()
        conn.close()
    pass


# 删除操作
def delete_sql(lastname):
    connection = connect()
    conn, cursor = connection['conn'], connection['cursor']

    sql_delete = "delete from persons where LastName=%s"
    try:
        cursor.execute(sql_delete, lastname)
        conn.commit()
        print('删除成功')
    except Exception as e:
        print('删除失败', e)
        conn.rollback()
    finally:
        cursor.close()
        conn.close()
    pass

SQL语句占位符的应用

1、完整的SQL语句，直接调用

sql_select = "select * from tablename"
cursor.execute(sql_select)

2、利用占位符传递参数。这里要注意，无论整数、字符串，占位符都为 %s，且不需加引号

在sql语句中借助占位符，组成完整SQL

tabel = 'persons'
sql = "select * from %s" % table
cursor.execute(sql)

参数替代

tabel = 'persons'
sql = "select * from %s" 
cursor.execute(sql， table)

# 参数多于1个时，execute()传入参数应为list或者tuple类型
sql_update = "update persons set birthday=%s where ID=%s"
cursor.execute(sql_update， ('2001/7/5', 3))

字典类型传递变量，这里要保证占位符的keys要包含在传递的字典keys中

# 这里的占位符%s修改为%(字典keyname)s
sql_insert = "insert into persons(ID, LastName, FirstName) " \
             "values (%(ID)s, %(LastName)s, %(FirstName)s)"
message = {
    "ID": 7,
    "LastName": "Jone",
    "FirstName": "Bob",
}
cursor.execute(sql_insert， message)