PHP MySQL Push and Pull from Database

Question

I am having a problem with my PHP code. I have a series of columns in MySQL database, PotVal, Current, ID, kWh and costKwh. Where ID is AUTO_INCREMENT, PotVal and Current are from a Text file - these are working correctly and storing the data fine. However i would like to take PotVal which is actually sensed power and convert this to KiloWatt hours using (PotVal*1)/(900) (don't worry I know its 1000 normally not 900) - this is also working fine and outputting the data in realtime, however I am trying to store this value in my kWh colum. Next I use this kWh column to carry out another calculation for cost per kWh using (kWh*18.56). However due to not storing data in kWh column I am getting 0.00 output and I can't rectify it!

So in summary why am I not able to store in kWh? And also I want to display the value to two decimal places but its actually displaying to six decimal places!

<?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);
?>

(I bet it's something simple... again!)

Answer 1

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

I think you already have a kWh column in received_data table, so you can not naming (PotVal/900) as kWh

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