使用 python 从数据库中重复 select 最新数据

Question

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

下面显示了从数据库中提取最后一行的代码。数据库每分钟获取一行新数据。

#!/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)

while循环的第一次迭代结果正确显示，但是结果没有更新到数据库中的最新数据集，它已经将行数据存储到变量中一次并且没有更新变量。

我得到的：

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

我想要得到的东西：

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

提前致谢

编辑添加 Table 条目的示例以伴随 post:

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 |

我运行 13:45 处的脚本，它收集具有 pi_id 的数据行：5768，然后一分钟后新的一行数据被输入到 table，当代码运行中的 While Loop 再次出现时，它会打印来自 的数据pi_id: 5768 而不是最新的数据 pi_id: 5769，这是我正在努力实现的。

Answer 1

我怀疑这不是一个完整的答案，但评论太长了。创建字典列表：

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)])

这将运行一次查询和 return 一个字典列表，您可以使用这些字典来按键访问值。就目前而言，没有真正需要迭代行，因为你有一个 LIMIT 1 但这会扩展。

Answer 2

我通过关闭数据库连接然后在 While 循环开始时重新连接来设法获得我需要的结果：

#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 的想法。

现在只是为了整理一下，所以它不是这样 convoluted/repetitive。

谢谢

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