当PHP中的启动时间大于1小时时，GET为空

Question

I have a table which calculates the cost based on time.I need to display table based on time with 1 hour limit. If time is greater than 1 hour it should display null in the cost column.How can I do that.

dashboard.php

        <?php
                    $host    = "localhost";
                    $user    = "root";
                    $pass    = "";
                    $db_name = "test2";
                    $lastId="";


                     $date = strtotime('now') - 3600;  
                     print_r($date);  
                     $week = strtotime('now') - 604800;  
                     $month = strtotime('now') - 2592000 ;        

                    //create connection
                    $con = mysqli_connect($host, $user, $pass, $db_name);

                    //test if connection failed
                    $result = mysqli_query($con,"SELECT SUM(cost) FROM track_data WHERE start_time > 
                      DATE_SUB(NOW(), INTERVAL 1 HOUR) ");

                    $result1 =  mysqli_query($con,"SELECT SUM(cost) FROM track_data WHERE start_time > 
                      DATE_SUB(NOW(), INTERVAL 1 WEEK)");

                    $result2 =  mysqli_query($con,"SELECT SUM(cost) FROM track_data WHERE start_time > 
                      DATE_SUB(NOW(), INTERVAL 1 MONTH)");


                    ?>

    <div class="col-md-6 col-md-offset-3">
            <table class="table table-hover table-striped">    
            <tr class="t_head"> 
              <th>  Days </th>
              <th> Usage  </th>
              <th> Total Cost  </th>

            </tr>       
    <?php


          while($row = mysqli_fetch_array($result))


    {



      echo "<tr id='emp_salary'>"; 

     echo "<td> Today </td>";
      echo "<td>1 Hour</td>";
    echo "<td>" .$row[0]. "</td>";

    echo "</tr>";
    }
?>
</table>
</div>

As u can see the above image the total cost column is empty. Instead of empty value I should get NUll or Zero.

Answer 1

You should use COALESCE

Because if your sql query returns no rows or the sum of rows is null then your echo will not actually echo anything.

Try this

$result = mysqli_query($con,"SELECT COALESCE(SUM(cost),0) FROM track_data 
WHERE start_time > DATE_SUB(NOW(), INTERVAL 1 HOUR) ");