在Python中，当变量为None时，是否有向PostgreSQL数据库输入NULL个键值的良好实践？
运行此查询:
mycursor.execute('INSERT INTO products (user_id, city_id, product_id, quantity, price) VALUES (%i, %i, %i, %i, %f)' %(user_id, city_id, product_id, quantity, price))
当user_id为None时，会导致TypeError异常.
当值为None时，如何使用psycopg2驱动程序将NULL插入数据库？
要向数据库中插入空值，有两个选项:
None另外:为了防止SQL注入，您不应该在查询中使用普通的字符串插值.
您应该将两(2)个参数传递给execute()，例如:
mycursor.execute("""INSERT INTO products
(city_id, product_id, quantity, price)
VALUES (%s, %s, %s, %s)""",
(city_id, product_id, quantity, price))
备选方案#2:
user_id = None
mycursor.execute("""INSERT INTO products
(user_id, city_id, product_id, quantity, price)
VALUES (%s, %s, %s, %s, %s)""",
(user_id, city_id, product_id, quantity, price))