If语句仅将新值写入Scrapy中的PostgreSQL db

import psycopg2

# 假设已经获取到了新值new_value

# 连接到PostgreSQL数据库
conn = psycopg2.connect(database="your_database", user="your_username", password="your_password", host="your_host", port="your_port")
cur = conn.cursor()

# 查询数据库中是否已存在该值
cur.execute("SELECT * FROM your_table WHERE value = %s", (new_value,))
existing_value = cur.fetchone()

# 如果数据库中不存在该值，则将其插入数据库
if existing_value is None:
    cur.execute("INSERT INTO your_table (value) VALUES (%s)", (new_value,))
    conn.commit()

# 关闭数据库连接
cur.close()
conn.close()