Select query executing twice - php

Question

I'm writing a simple page to retrieve "PO Numbers" that belong to the logged-in user. That portion is working fine with the exception of the query returning 2 complete sets of records. I have checked for page refresh issues, as mentioned in other posts I've read, but none have been found.
poTable.php
<table class="table" style="width: 100%">
<thead class="thead-dark">
<tr>
<th scope="col">PO#</th>
<th scope="col">Job#</th>
<th scope="col">Job Name</th>
<th scope="col">Salesperson</th>
<th scope="col">Vendor</th>
<th scope="col">Date</th>
</tr>
</thead>
<tbody>
<?php include 'usersPOs.php'?>
</tbody>
</table>
usersPOs.php
$db = mysqli_connect('localhost', 'root', '', 'acs-jobs-pos');
$userID = $_SESSION['userID'];
$userPrivs = $_SESSION['admin'];
if ($userPrivs == 0) { // User IS NOT an admin
// Get ALL main table records that belong to the logged-in user
$sqlmain = "SELECT * FROM main INNER JOIN users ON main.userID = '" . $userID . "'";
//debug_print_backtrace();
$resultmain = mysqli_query($db,$sqlmain);
while($rowmain = mysqli_fetch_assoc($resultmain))
{
?>
<tr>
<?php
$PONumb = $rowmain["PONumb"];
$jobNumber = $rowmain["jobNumber"];
$jobName = $rowmain["jobName"];
$salespersonID = $rowmain["salespersonID"];
$vendorID = $rowmain["vendorID"];
$timestamp = $rowmain["timestamp"];
?>
<td><?php echo $PONumb ?></td>
<td><?php echo $jobNumber ?></td>
<td><?php echo $jobName ?></td>
<?php
$sqlsp = "SELECT * FROM users WHERE userID = '" . $salespersonID . "'";
$resultsp = mysqli_query($db,$sqlsp);
$rowsp = mysqli_fetch_assoc($resultsp);
if ($rowsp["lastname"] == '' && $rowsp["firstname"] == '') {
?>
<td></td>
<?php
} else {
?>
<td><?php echo $rowsp["lastname"] . ', ' . $rowsp["firstname"] ?></td>
<?php
}
$sqlvendor = "SELECT * FROM vendor
WHERE vendorID = '" . $vendorID . "'";
$resultvendor = mysqli_query($db,$sqlvendor);
$rowvendor = mysqli_fetch_assoc($resultvendor);
?>
<td><?php echo $rowvendor["vendorname"] ?></td>
<td><?php echo $timestamp ?></td>
</tr>
<?php
}
mysqli_close($db);
}

Answer 1

This code could be hugely simplified by use of joins. I'd also recommend using PDO for your database access; it's less verbose and makes prepared statements easier (and those are not optional in any environment.) Only relevant columns are selected from the database. A heredoc block is also used to simplify output.
<?php
$db = new PDO('mysql:host=localhost;dbname=acs-jobs-pos', 'root', '');
$userID = $_SESSION['userID'];
$userPrivs = $_SESSION['admin'];
if ($userPrivs == 0) {
$sql = "SELECT m.PONumb, m.jobNumber, m.jobName, m.salespersonID, m.vendorID, m.timestamp,
u.lastname, u.firstname, v.vendorname
FROM main m
LEFT JOIN users u ON (m.salespersonID = u.userID)
LEFT JOIN vendors v ON (m.vendorID = v.vendorID)
WHERE m.userID = ?";
$stmt = $db->prepare($sql);
$stmt->execute([$userID]);
$results = $stmt->fetchAll(\PDO::FETCH_ASSOC);
foreach ($results as $row) {
echo <<< HTML
<tr>
<td>$row[PONumb]</td>
<td>$row[jobNumber]</td>
<td>$row[jobName]</td>
<td>$row[lastname], $row[firstname]</td>
<td>$row[vendorname]</td>
<td>$row[timestamp]</td>
</tr>
HTML;
}
}

Answer 2

follow sql error
"SELECT * FROM main INNER JOIN users ON main.userID = '" . $userID . "'";
you can not use join as this, something like
"SELECT * FROM main INNER JOIN users ON main.userID = users.ID where users.ID='" . $userID . "'";