1064 error, Not sure what the issue is - php

Question

I keep getting this error when submitting. I have checked my form 10x and I cannot figure out what is wrong with it.
Here is the error
SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE order_num = '5293528'' at line 1
Here is the form code
public function next()
{
try
{
if(isset($_POST['giventoatpdate']))
{
$update = trim($_POST['update']);
$orders = $_SESSION['order_nums'];
$st=$this->db->prepare("INSERT INTO `orders` (giventoatpdate) VALUES (:upd) WHERE order_num = :orderr");
$st->bindparam(":upd", $update);
$st->bindparam(":orderr", $orders);
$st->execute();
return $st;
}
$order = $_GET['uid'];
$stmt=$this->db->prepare("SELECT * FROM orders WHERE order_num = :order");
$stmt->execute(array(":order"=>$order));
$row=$stmt->fetch(PDO::FETCH_ASSOC);
if($row['giventoatpdate'] = ' ')
{
echo
"
<form name='atpdate' method='POST'>
Date Sent to clown?
<br>
<input type='text' name='update'>
<br>
<input type='submit' name='giventoatpdate'>
</form>
";
}
Everything else is working fine. It gives me this error when I hit submit.

Answer 1

Seeing somebody popped in an answer...
It's because INSERT doesn't have a WHERE clause.
Now read the manual http://dev.mysql.com/doc/en/insert.html
INSERT ... ON DUPLICATE KEY UPDATE does.
http://dev.mysql.com/doc/refman/5.7/en/insert-on-duplicate.html
Or, you may have intended to do an UPDATE. http://dev.mysql.com/doc/en/update.html
Seeing $update = trim($_POST['update']); the operative word being "update" in the POST array, I'm thinking you want to do an UPDATE here rather than an INSERT, since you are dealing with orders taken from your site.
So, you have a few choices here.
If it's an UPDATE, your query would read as:
UPDATE `orders`
SET giventoatpdate = :upd
WHERE order_num = :orderr
Check for errors:
http://php.net/manual/en/pdo.error-handling.php
Add error reporting to the top of your file(s) which will help find errors.
<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
// Then the rest of your code
Sidenote: Displaying errors should only be done in staging, and never production.
Footnotes:
Seeing if($row['giventoatpdate'] = ' ') you do realize that this checks for a "space" rather than if($row['giventoatpdate'] = '') to check if it's "empty".
You're also "assigning" rather than doing a "comparison" here which should read as:
if($row['giventoatpdate'] == '')
If you're checking for empty'ness, then remove the space in there, or you can do
if(empty($row['giventoatpdate']))
References:
http://php.net/manual/en/language.operators.assignment.php
http://php.net/manual/en/language.operators.comparison.php
http://php.net/manual/en/function.empty.php

Answer 2

INSERT doesn't have WHERE operator.
You need to change query to something like this:
UPDATE myTable SET my_field = :new_value WHERE my_another_filed = :another_value_or_row_id