我的 PHP 代码有问题。我在 MySQL 数据库中有一系列列，PotVal、Current、ID、kWh 和 costKwh。其中 ID 是 AUTO_INCREMENT，PotVal 和 Current 来自文本文件 - 它们工作正常并且可以很好地存储数据。但是我想使用 PotVal，它实际上是感测到的功率，并使用 (PotVal*1)/(900) 将其转换为千瓦小时(别担心，我知道它的 1000 通常不是 900)——这也工作正常并输出实时数据，但是我试图将此值存储在我的千瓦时列中。接下来，我使用此 kWh 列使用 (kWh*18.56) 对每 kWh 成本进行另一次计算。但是，由于没有将数据存储在 kWh 列中，我得到 0.00 输出并且我无法纠正它!

总而言之，为什么我不能以 kWh 为单位存储？而且我想将值显示到小数点后两位，但它实际上显示到小数点后六位!

<?php 

header('Refresh: 1.5');

// Set relevent pseudo-variables
    $hostname = 'localhost';
    $username = 'root';
    $password = '';
    $table = 'received_data';
    $drop = 'DROP TABLE received_data';
    $iwemsdatafile = 'IWEMSData.txt';

// Connect to MySQL

    $dbconnect = mysql_connect($hostname, $username, $password)
        or die('Unable to connect to MySQL: ' . mysql_error());
    //  echo 'Connected to MySQL<br>';

    mysql_query($drop);

// Create database, table and columns

    $cdb = 'CREATE DATABASE IWEMS_Data';
    //  echo 'IWEMS_Data has been created<br /><hr />';

    $selectdb = mysql_select_db('IWEMSData',$dbconnect)
        or die('Could not select IWEMSData');
    //  echo 'Connected to IWEMSData database<br />';

    mysql_query($drop);

    $ctb = 'CREATE TABLE received_data
    (
    Current DECIMAL(30,2) NOT NULL,
    PotVal DECIMAL(30,2) NOT NULL,
    kWh DECIMAL(30,2) NOT NULL,
    costkWh DECIMAL(30,2) NOT NULL,
    ID BIGINT NOT NULL AUTO_INCREMENT,
    PRIMARY KEY(ID,PotVal,Current)
    )';

    mysql_query($ctb, $dbconnect);
    //  echo 'Received_Data Table has been created<br />';
    //  echo 'Current, PotVal and ID columns have been created<br /><hr />';

// Push IWEMSData.txt data into MySQL database

    mysql_query
    ('
    LOAD DATA LOCAL INFILE "IWEMSData.txt" 
    REPLACE INTO TABLE received_data 
    FIELDS TERMINATED BY " " 
    LINES TERMINATED BY "\\r\\n"
    (PotVal, Current)
    ;')
    or die('Error Loading Data File.<br>' . mysql_error());

// Pull IWEMSData from MySQL database

    $seldat = 'SELECT * FROM received_data ORDER BY ID DESC LIMIT 1';


    $data = mysql_query($seldat) 
        or die('Error retrieving data: ' . mysql_error());

// Display data on web browser

    while ($finalrow = mysql_fetch_array($data))
    {
        echo '<hr /> Apparent Power<br />';
        echo $finalrow['PotVal'];
        echo ' Watts';
        echo '<br /><hr />';
        echo 'Detected Current<br />';
        echo $finalrow['Current'];
        echo ' Amps';
        echo '<br /><hr />';
    }

// Display per kWh data on web browser

    $perkWh = 'SELECT *, (PotVal/900) AS kWh
    FROM received_data ORDER BY ID DESC LIMIT 1';

    $qperkWh =mysql_query($perkWh) or die('Error');

    while ($finalkWh = mysql_fetch_array($qperkWh))
    {
    echo 'kWh<br />';
    echo $finalkWh['kWh'];
    echo '<br /><hr />';
    }


// Display cost per kWh data on web browser

    $cperkWh = 'SELECT *, (kWh*18.67) AS costkWh
    FROM received_data ORDER BY ID DESC LIMIT 1';

    $cqperkWh =mysql_query($cperkWh) or die('Error');

    while ($cfinalkWh = mysql_fetch_array($cqperkWh))
    {
    echo 'Cost kWh<br />';
    echo $cfinalkWh['costkWh'];
    echo '<br /><hr />';
    }

// Close Database connection when complete

    mysql_close($dbconnect);
?>

(我敢打赌这很简单……又一次!)

最佳答案

$perkWh = 'SELECT *, (PotVal/900) AS kWh
FROM received_data ORDER BY ID DESC LIMIT 1';

我认为您在 received_data 表中已经有一个 kWh 列，因此您不能将 (PotVal/900) 命名为 千瓦时

同样的问题在 $cperkWh = 'SELECT *, (kWh*18.67) AS costkWh FROM received_data ORDER BY ID DESC LIMIT 1'; 与 costkWh

关于PHP MySQL 从数据库推送和拉取，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16166257/