如何使用 python3 将值插入到 sql 表中？

Question

我正在尝试使用 Paho 库设置 MQTT 客户端。这样就没有问题了，但我正在尝试将收到的发布插入到 sql 数据库中。我正在将接收到的有效负载字符串转换为字典并添加一些条目。执行以下代码时：

def insert_values(db_connection=None, topic=None, payload=None, time_received=None):
    query_1 = "SELECT topic_id FROM topics WHERE topic = %s"
    query_2 = """INSERT INTO measurements (start_time, end_time, value, max_value, min_value, time_received, topic_id)
                 VALUES (%(start_time)s, %(end_time)s, %(value)s, %(max_value)s, %(min_value)s, %(time_received)s, 
                        %(topic_id)s)"""
    cursor = db_connection.cursor(prepared=True)
    topic_id = cursor.execute(query_1, topic)
    payload["time_received"] = time_received
    payload["topic_id"] = topic_id
    cursor.executemany(query_2, payload)
    db_connection.commit()
    db_disconnect(db_connection, cursor)

我收到以下错误：

Caught exception in on_message: 1210: Incorrect number of arguments executing prepared statement

有效载荷如下所示：

payload = {
        "Starttime:": 2020-02-18 10:11:22.2145563,
        "Endtime:": 2020-02-18 10:12:22.2145563,
        "Average Humidity:": 44.256241,
        "Number of Values:": 22,
        "Max Humidity:": 44.586214,
        "Min Humidity:": 44.012148521)
}

加上一些额外的信息，比如收到有效载荷的时间。在 insert_values 方法中，我试图从表主题中获取 topic_id 并将其写入有效负载。

编辑：要写入测量值的表格如下所示：

CREATE TABLE IF NOT EXISTS measurements
(measurement_id INT AUTO_INCREMENT,
 start_time DATETIME,
 end_time DATETIME,
 value FLOAT,
 max_value FLOAT,
 min_value FLOAT,
 time_received DATETIME,
 topic_id INT,
 PRIMARY KEY (measurement_id),
 FOREIGN KEY (topic_id) REFERENCES topics(topic_id))

Answer 1

您的有效负载有 6 个键，然后您添加另外 2 个使其成为 8 在您的查询中，您只有 7 个参数 我不确定，但我认为您忘记添加“平均湿度” 编辑：看到你的桌子 DESC 后

    query_2 = """INSERT INTO measurements (start_time, end_time, value, max_value, min_value, time_received, topic_id)
             VALUES (%s,%s,%s,%s,%s,%s,%s)"""
cursor = db_connection.cursor(prepared=True)
topic_id = cursor.execute(query_1, topic)
payload["time_received"] = time_received
payload["topic_id"] = topic_id
payload.pop("Average Humidity:", None)
cursor.executemany(query_2, payload)
db_connection.commit()
db_disconnect(db_connection, cursor)

Answer 2

这里：

"""VALUES (%(start_time)s, %(end_time)s, %(value)s, %(max_value)s, %(min_value)s, %(time_received)s, %(topic_id)s)"""

这里：

payload = {
    "Starttime:": 2020-02-18 10:11:22.2145563,
    "Endtime:": 2020-02-18 10:12:22.2145563,
    "Average Humidity:": 44.256241,
    "Number of Values:": 22,
    "Max Humidity:": 44.586214,
    "Min Humidity:": 44.012148521)
}

您的 payload 键必须与查询的占位符名称匹配 - 或者您的占位符与 payload 键匹配。您的数据库客户端绝对不会尝试猜测“start_time”和“Starttime”实际上应该是同一件事。当然，您必须有 all 查询占位符的数学键。