Merge column entries in mysql - php

Question

PeterM helped me with this question, but i dont want to create new one, thats why im editing this one.
I got another problem, sorry, im just new with sql.
This is my code that output all the information I need from the database.
What i want:
I created table with name "customers" with columns "id and customername".
Then i created simple script with INSERT INTO "customers", yes, its script like admin page.
The idea is: I want to add new orders from a separate page, for example: admin.php so I don't have to do it from a file.
How to easily do this?
I have admin.php file with: INSERT INTO customers (customername) VALUES (customername) and its working, i can add new order to database, when i fill html form, it doesn't show my new added order.
<?php
$output = "SELECT *, SUM(enddate - startdate) AS time FROM employees GROUP
BY id";
$result = mysqli_query($conn, $output);
WHILE ($row = mysqli_fetch_assoc($result)) {
$EMPLOYEE = $row['employee'];
$CUSTOMER = $row['customername'];
$WORKDATE = $row['workdate'];
$WORKTYPE = $row['worktype'];
$DAYHOURS = $row['startdate'];
$ENDDATE = $row['enddate'];
$TOTAL = $row['time'];
echo "
<tr>
<td>$EMPLOYEE</td>
<td>$CUSTOMER</td>
<td>$WORKDATE</td>
<td>$WORKTYPE</td>
<td>$DAYHOURS</td>
<td>$ENDDATE</td>
<td>$TOTAL</td>
</tr>";
}
?>
My html form:
<div class='row'>
<div class='col-25'>
<label for='customers'>Choose OrderName</label>
</div>
<div class='col-75'>
<select name='customername'>
<?php
$customers = "SELECT customername FROM customers";
$result = mysqli_query($conn, $customers);
WHILE ($row = mysqli_fetch_assoc($result)) {
$customer = $row['customername'];
echo "<option value=''>$customer</option>";
}
?>
</select>
</div>
</div>

Answer 1

You should change your query into something like this:
SELECT *, SUM(`enddate` - `startdate`) AS time FROM `employees` GROUP BY `employee`;
First you need to subtract the startdate from the enddate then get the sum of all the grouped results, hence the SUM part.
This should give you a result somewhat similar to this
Results:
| id | employee | startdate | enddate | time |
|----|----------|-----------|---------|------|
| 8 | David | 8 | 22 | 17 |
The time column is the one you need.
I made a fiddle where you can see and test how it works, http://sqlfiddle.com/#!9/40a959/5