Question

我正在尝试使用python将数据库中的最新数据存储在变量中，但是脚本在执行时存储的是数据行，而不是最新的数据集。

以下显示了从数据库中提取最后一行的代码。数据库每分钟都会获得新的一行数据。

#!/usr/bin/env python

#import required modules
from time import sleep
import MySQLdb


#set MySQL Variables
host = "localhost"
user = "user"
password = "pass"
schema = "schema"

#connect to MySQL
db = MySQLdb.connect(host, user, password, schema)
curs = db.cursor()

#Define Sql Queries to Read the last Value in the Database
sqlT="SELECT temperature FROM system_info ORDER BY pi_id DESC LIMIT  1"
sqlH="SELECT humidity FROM system_info ORDER BY pi_id DESC LIMIT 1"
sqlIP="SELECT ip_address FROM system_info ORDER BY pi_id DESC LIMIT 1"
sqlDI1="SELECT DI1 FROM system_info ORDER BY pi_id DESC LIMIT 1"
sqlDI2="SELECT DI2 FROM system_info ORDER BY pi_id DESC LIMIT 1"
sqlDI3="SELECT DI3 FROM system_info ORDER BY pi_id DESC LIMIT 1"
sqlDI4="SELECT DI4 FROM system_info ORDER BY pi_id DESC LIMIT 1"
sqlDI5="SELECT DI5 FROM system_info ORDER BY pi_id DESC LIMIT 1"
sqlDI6="SELECT DI6 FROM system_info ORDER BY pi_id DESC LIMIT 1"
sqlDI7="SELECT DI7 FROM system_info ORDER BY pi_id DESC LIMIT 1"
sqlDI8="SELECT DI8 FROM system_info ORDER BY pi_id DESC LIMIT 1"

#Begin Script Infinitely
while True:
        #Gather Values from Database
        curs.execute(sqlT)
        lastT = curs.fetchone()
        for Temp in lastT:
                temp_reading = Temp
        curs.execute(sqlH)
        lastH = curs.fetchone()
        for Hum in lastH:
                hum_reading = Hum
        curs.execute(sqlDI1)
        lastDI1 = curs.fetchone()
        for DI1 in lastDI1:
                DI1_reading = DI1
        curs.execute(sqlDI2)
        lastDI2 = curs.fetchone()
        for DI2 in lastDI2:
                DI2_reading = DI2
        curs.execute(sqlDI3)
        lastDI3 = curs.fetchone()
        for DI3 in lastDI3:
                DI3_reading = DI3
        curs.execute(sqlDI4)
        lastDI4 = curs.fetchone()
        for DI4 in lastDI4:
                DI4_reading = DI4
        curs.execute(sqlDI5)
        lastDI5 = curs.fetchone()
        for DI5 in lastDI5:
                DI5_reading = DI5
        curs.execute(sqlDI1)
        lastDI6 = curs.fetchone()
        for DI6 in lastDI6:
                DI6_reading = DI6
        curs.execute(sqlDI1)
        lastDI7 = curs.fetchone()
        for DI7 in lastDI7:
                DI7_reading = DI7
       curs.execute(sqlDI8)
       lastDI8 = curs.fetchone()
       for DI8 in lastDI8:
                DI8_reading = DI8

        #Print Values
        print(temp_reading)
        print(hum_reading)
        print(DI1_reading)
        print(DI2_reading)
        print(DI3_reading)
        print(DI4_reading)
        print(DI5_reading)
        print(DI6_reading)
        print(DI7_reading)
        print(DI8_reading)

        #Rest so Values change
        sleep(61)

对于while循环的第一次迭代，结果正确显示，但是结果不会更新到数据库中的最新数据集，它已将行数据存储到变量中一次，并且不会更新变量

我得到的是

22
45
Open
Open
Open
Open
Open
Open
Open
Open
22
45
Open
Open
Open
Open
Open
Open
Open
Open

我想要得到什么：

22
45
Open
Open
Open
Open
Open
Open
Open
Open
25
56
Open
Open
Closed
Open
Open
Open
Open
Open

预先感谢

EDIT 在表条目的示例中添加帖子：

pi_id | time | ip_address | temperature | humidity | DI1 | DI2 | DI3 | DI4 | DI5 | DI6 | DI7 | DI8 |
5768  | 13:45 | 10.0.0.1 |   22   |   45   | Open | Open | Open | Open | Open | Open | Open | Open |
5769  | 13:46 | 10.0.0.1 |   25   |   56   | Open | Open | Closed | Open | Open | Open | Open | Open |

我在13:45运行脚本，它使用 pi_id：5768 收集数据行，然后在一分钟后，当代码中的循环再次运行时，它将打印 pi_id：5768 中的数据，而不是最新数据 pi_id：5769 ，这就是我的意思试图实现。

Answer 1

我设法通过关闭数据库连接，然后在While循环的开头重新连接来获得所需的结果：

#Begin Script Infinitely
while True:

    #Connect/Re-connect to database
    db = MySQLdb.connect(host, user, password, schema)

    #Define Cursor
    curs = db.cursor()

    #Gather Values from Database
    curs.execute(sqlT)
    lastT = curs.fetchone()
    for Temp in lastT:
        temp_reading = Temp
    curs.execute(sqlH)
    lastH = curs.fetchone()
    for Hum in lastH:
        hum_reading = Hum
    curs.execute(sqlDI1)
    lastDI1 = curs.fetchone()
    for DI1 in lastDI1:
        DI1_reading = DI1       
    curs.execute(sqlDI2)
    lastDI2 = curs.fetchone()
    for DI2 in lastDI2:
        DI2_reading = DI2
    curs.execute(sqlDI3)
    lastDI3 = curs.fetchone()
    for DI3 in lastDI3:
        DI3_reading = DI3
    curs.execute(sqlDI4)
    lastDI4 = curs.fetchone()
    for DI4 in lastDI4:
        DI4_reading = DI4
    curs.execute(sqlDI5)
    lastDI5 = curs.fetchone()
    for DI5 in lastDI5:
        DI5_reading = DI5
    curs.execute(sqlDI6)
    lastDI6 = curs.fetchone()
    for DI6 in lastDI6:
        DI6_reading = DI6
    curs.execute(sqlDI7)
    lastDI7 = curs.fetchone()
    for DI7 in lastDI7:
        DI7_reading = DI7
    curs.execute(sqlDI8)
    lastDI8 = curs.fetchone()
    for DI8 in lastDI8:
        DI8_reading = DI8   

    #Close Cursor
    curs.close()

    #Disconnect from Database
    db.close()

    #Print Values
    print(temp_reading)
    print(hum_reading)
    print(DI1_reading)
    print(DI2_reading)
    print(DI3_reading)
    print(DI4_reading)
    print(DI5_reading)
    print(DI6_reading)
    print(DI7_reading)
    print(DI8_reading)

    #Rest so Values change
    sleep(60)

感谢@ Iandru27和@Rick James传达了这个想法。

现在只是将所有内容整理整齐，这样就不会那么令人费解/重复。

谢谢

Answer 2

我怀疑这不是一个完整的答案，但发表评论的时间太长了。创建词典列表：

data = []
c.execute("""SELECT * FROM system_info ORDER BY pi_id DE0SC LIMIT 1""")
headers = [item[0] for item in c.description] # List comprehension
for row in c.fetchall():
    data.append([dict(zip(headers, row)])

这将运行一次查询并返回字典列表，您可以使用该字典通过键访问值。就目前而言，由于您有LIMIT 1，所以实际上不需要迭代行。

使用python

2 个答案: