Variable not recognised in INSERT but working in SELECT - php

Question

Basically I am using the variable $shopid to recognise which shop has been chosen. I am now trying to create a comment system to enable each shop page to be commented on. My SELECT query is recognising $shopid and enabling me to use it, when I try to use the same variable in my INSERT, it simply posts 0.
<?php
database connection
session_start();
if (isset($_SESSION['logged'])){
$s_userID = $_SESSION['userID'];
$shopid = $_GET['page_id'];
$str_shops = '';
//bring shop data
mysqli_select_db($db_server, $db_database);
$query = "SELECT * FROM shops WHERE shopID = '$shopid'";
$result = mysqli_query($db_server, $query);
if (!$result) die("Database access failed: " . mysqli_error($db_server));
while($row = mysqli_fetch_array($result)){
$str_shops .= "<div class='result'><strong>" .
$row['image1'] . "<br><br>" .
$row['name'] . "</strong><br><br>" .
$row['address'] . "<br><br>" .
$row['website'] . "<br><br>" .
$row['openinghours'] . "<br><div class='justifytext'>" .
$row['more'] . "<br><br></div><strong>What do they sell?</strong><br><br><div class='justifytext'>" .
$row['sold'] . "<br><br></div></div>";
}
//post comment
mysqli_select_db($db_server, $db_database);
$comment = $_POST['comment'];
if ($comment != '') {
$query = "INSERT INTO comments (userID,shopID,comment) VALUES ('$s_userID', '$shopid', '$comment')";
mysqli_query($db_server, $query) or
die("Insert failed: " . mysqli_error($db_server));
$commentmessage = "Thanks for your comment!";
}
mysqli_select_db($db_server, $db_database);
$query = "SELECT * FROM comments";
$result = mysqli_query($db_server, $query);
if (!$result) die("Database access failed: " . mysqli_error($db_server)); $i = 0;
while($row = mysqli_fetch_array($result)){ $i++;
$str_comments.= "<p><div id='displaycomments'>" . $row['username']. ", " .
$row['commdate'] . ": <br>" .
$row['comment'] . "</div>";
}
}
echo $str_shops;
echo $commentmessage;
echo $str_comments;
mysqli_close($db_server);
?>
Can anyone see why this isn't working? I'm not getting an error, it is simply adding 0 to the shopID column in my table.

Answer 1

My guess would be that your shopID column would be of INT datatype and you are passing a string to it in your insert statement, thats why 0 is being stored.Try again by removing the single quotes around $shopid, like this-
INSERT INTO comments (userID,shopID,comment) VALUES ('$s_userID', $shopid, '$comment')"
^^^^^^^ remove the single quotes