如何根据上一次和最后一次更改的值构建新的日期列？

import mysql.connector

# 连接到MySQL数据库
cnx = mysql.connector.connect(user='your_username', password='your_password',
                              host='your_host', database='your_database')
cursor = cnx.cursor()

# 创建新的日期列
alter_table_query = "ALTER TABLE your_table ADD new_date_column DATE"
cursor.execute(alter_table_query)

# 查询数据集并按照某一列排序
select_query = "SELECT * FROM your_table ORDER BY some_column"
cursor.execute(select_query)
rows = cursor.fetchall()

# 初始化上一次更改的日期值
last_change_date = None

# 遍历数据集并更新日期列
for row in rows:
    current_value = row[0]  # 假设要比较的值在第一列
    current_date = row[1]  # 假设日期值在第二列

    if current_value == last_change_value:
        update_query = "UPDATE your_table SET new_date_column = %s WHERE some_column = %s"
        cursor.execute(update_query, (last_change_date, current_value))
    else:
        update_query = "UPDATE your_table SET new_date_column = %s WHERE some_column = %s"
        cursor.execute(update_query, (current_date, current_value))
        last_change_date = current_date

# 提交更改并关闭数据库连接
cnx.commit()
cursor.close()
cnx.close()