function unable to call WHERE id = $id - php

Question

I'm trying to do a multiple edit function, the code goes through but the database is not updated. I figure the problem is that at WHERE id = $id no value gets called out because if I replace $id with an actual id e.g. id = 001 the entry 001 gets updated.
This page selects which entries get edited
<?php
if (!mysqli_connect_errno($con)) {
$queryStr = "SELECT * " . "FROM crewlist";
}
$result = mysqli_query($con, $queryStr);
while ($row = mysqli_fetch_array($result)) {
if (date("Y-m-d") > $row['start_date'] && date("Y-m-d") < $row['end_date']) {
echo "<tr><th>" . "<input type = 'checkbox' name = 'checkbox2[]' value='" . $row['crew_name']. "' >" . "</th>";
echo "<th>" . "" . $row["crew_name"] . "";
echo "<th>" . $row["crew_rank"] . "</th>";
echo "<th>" . $row["start_date"] . "</th>";
echo "<th>" . $row["end_date"] . "</th>";
echo "<th>" . $row["watchkeeping"] . "</th>";
echo "<th>" . $row["active"] . "</th>";
} else {
}
}
?>
This is the edit page
<?php include 'header.php'; ?>
<div id="container4"><?php
require ("dbfunction.php");
$con = getDbConnect();
$checkbox2 = $_POST['checkbox2'];
if (!mysqli_connect_errno($con)) {
$str = implode($checkbox2);
$queryStr = "SELECT * " .
"FROM crewlist WHERE ($str) && crew_id";
}
$result = mysqli_query($con, $queryStr);
?><form action="handlemultiedit.php" method="post"><?php
if ($_POST['submit']) {
$checkbox2 = $_POST['checkbox2'];
foreach ($checkbox2 as $crewname) {
?>
<input type="hidden" name="crew_id" value="<?php $id = isset($_GET['id']) ? $_GET['id'] : ''; ?>" />
<?php echo "<tr><th>" . $crewname . ":</th><br>";
echo " <tr>
<td>Shift 1:</td>
<td><input type=\"time\" name=\"start_hour\" value=\"start_hour\" id=\"start_hour\" step=\"1800\" required> to <input type=\"time\" name=\"end_hour\" value=\"end_hour\" id=\"end_hour\" step=\"1800\" required>
</td>
</tr>
<tr>
<td>Shift 2:</td>
<td><input type=\"time\" name=\"start_hour2\" value=\"start_hour2\" id=\"start_hour2\" step=\"1800\" required> to <input type=\"time\" name=\"end_hour2\" value=\"end_hour2\" id=\"end_hour2\" step=\"1800\" required>
</td>
</tr><br><br>";
?><?php
}?><td><input type="submit" value="Submit" ></td></form><?php
}
?>
print_r($_POST);
require 'dbfunction.php';
$con = getDbConnect();
$crew_id = $_POST["crew_id"];
$start_hour = $_POST["start_hour"];
$end_hour = $_POST["end_hour"];
$start_hour2 = $_POST["start_hour2"];
$end_hour2 = $_POST["end_hour2"];
if (!mysqli_connect_errno($con)) {
$sqlQueryStr = "UPDATE crewlist SET start_hour = '$start_hour',end_hour = '$end_hour', start_hour2 = '$start_hour2',end_hour2 = '$end_hour2' WHERE crew_id = $crew_id";
mysqli_query($con, $sqlQueryStr);
}
//header('Location: crewlisting.php');
mysqli_close($con);
?>

Answer 1

Try placing single quotes (i.e. 's) around your final variable in your statement, as you have done with all of your other variables, i.e. change it to "WHERE crew_id = '$crew_id'";