Database Query failed error when inserting Row into Table - php

Question

I am getting Database query failed error while trying to insert a new row into a table. This table (pages) has a column (subject_id) referencing another table (subjects). I am passing the value of the of the subject_id from the url and it is passed on the form correctly. All the values seem to be passed correctly on the form using php, but i get error while i try to insert the row. The form submits to itself.
select_all_pages_by_subject($sid) is a function that selects all rows (pages) from the current subject (passed from the url). It works fine for the position field.
I suspect this error is probably a MySQL syntax error somewhere in my code, but i just cant seem to figure it out yet. I appreciate some help. Thank you.
Here is my code:
<div class="body_content">
<?php
$sid = null;
if(isset($_GET["subject"])) {
$sid = $_GET["subject"];
}
?>
<form action="create_page.php" method="post">
Menu Name: <input type="text" name="menu" /> <br>
Position: <select name="position">
<?php
$new_page_query = select_all_pages_by_subject($sid);
$page_count = mysqli_num_rows($new_page_query);
for($count=1; $count<=($page_count + 1); $count++) {
echo "<option value=\"$count\">$count</option>";
}
?>
</select> <br>
Visible:<br>
No <input type="radio" name="visible" value="0" />
Yes <input type="radio" name="visible" value="1" /> <br>
Subject ID: <input type="text" name="subject_id" value="<?php echo $sid; ?>" /> <br>
Content: <br>
<textarea rows="5" cols="40" name="content"></textarea> <br>
<input type="submit" value="Create Page" name="submit" /> <br>
Cancel <br>
</form>
<?php
if(isset($_POST['submit'])) {
$menu_name = $_POST["menu"];
$position = (int) $_POST["position"];
$visible = (int) $_POST["visible"];
$content = $_POST["content"];
$subject_id = (int) $_POST["$sid"];
$insert_query = "INSERT INTO pages (subject_id, menu_name, position,
visible, content) VALUES ({$subject_id},'{$menu_name}', {$position},
{$visible}, '{content}')";
$page_insert = mysqli_query($connection, $insert_query);
if($page_insert) {
$_SESSION["message"] = "Page created successfully";
redirect_to("admin.php");
} else {
$_SESSION["message"] = "Page creation failed";
redirect_to("create_page.php?subject=$sid");
}
}
?>
</div>
Edit: removed the WHERE statement

Answer 1

The problem is INSERT cannot have a WHERE after it.
$insert_query = "INSERT INTO pages (subject_id, menu_name, position, visible, content) VALUES ({$subject_id},'{$menu_name}', {$position}, {$visible}, '{content}')";

Answer 2

So after some troubleshooting, i decided to separate the form and form processing into 2 different pages, then i realized the problem, in the form action, i did not specify the subject id in the URL since i was passing the id from the URL:
<form action="create_page.php" method="post">
should be:
<form action="create_page.php?subject=<?php echo $sid; ?>" method="post">
Edit: I have also noticed that the "Database query failed" error was being called on the Position form field where i was making a database connection on the "pages" table to pull the number of rows. So when the insert statement failed due to the absence of subject id from the url, php did not process the page past the position form field, it called the error on the field and stopped execution. When insert query fails, parts of the form are displayed on the screen (only the menu name field and the position field with empty values). When i tried to view source code for errors, it requested the page be reloaded again (felt like an infinite loop running or something)