My PHP PDO update counter in MYSQL does +3 instead of +1? - php

Question

I want to count the amount of updates made on a record. The field name is pm_v. I got the following codes:
Update function:
function update_products_materials(){
$query = "UPDATE
" . $this->table_name . "
SET
pm_id = :pm_id1,
pm_code = :pm_code,
pm_name = :pm_name,
pm_department = :pm_department,
pm_temp = :pm_temp,
pm_color = :pm_color,
pm_v = pm_v +1
WHERE
pm_id = :pm_id2";
$stmt = $this->conn->prepare($query);
$this->pm_id=htmlspecialchars(strip_tags($this->pm_id));
$this->pm_code=htmlspecialchars(strip_tags($this->pm_code));
$this->pm_name=htmlspecialchars(strip_tags($this->pm_name));
$this->pm_department=htmlspecialchars(strip_tags($this->pm_department));
$this->pm_temp=htmlspecialchars(strip_tags($this->pm_temp));
$this->pm_color=htmlspecialchars(strip_tags($this->pm_color));
$stmt->bindParam(':pm_id1', $this->pm_id);
$stmt->bindParam(':pm_id2', $this->pm_id);
$stmt->bindParam(':pm_code', $this->pm_code);
$stmt->bindParam(':pm_name', $this->pm_name);
$stmt->bindParam(':pm_department', $this->pm_department);
$stmt->bindParam(':pm_temp', $this->pm_temp);
$stmt->bindParam(':pm_color', $this->pm_color);
$stmt->execute();
return $stmt;
}
This is the only place where I use pm_v.
The function is called in the following code:
$database = new Database();
$db = $database->getConnection();
// initialize objects
$products_materials = new Products_Materials($db);
$products_materials->id = $id;
$products_materials->view_products_materials();
$products_materials->update_products_materials();
if(isset($_POST["update"])){
$products_materials->pm_id=$id;
$products_materials->pm_code=$_POST['pm_code'];
$products_materials->pm_name=$_POST['pm_name'];
$products_materials->pm_department=$_POST['pm_department'];
$products_materials->pm_temp=isset($_POST['pm_temp']) ? $_POST['pm_temp'] : '';
$products_materials->pm_color=isset($_POST['pm_color']) ? $_POST['pm_color'] : '';
if($products_materials->update_products_materials() && (isset($_POST["update"]))){
header("Location: view_products_materials.php?id={$id}");
$_POST=array();
} else {
echo "<div class='alert alert-danger' role='alert'>Unable to save record.</div>";
}
}
Somehow, when I update a record it does +3 instead of +1. Can anyone explain why this is happening and how I can get it right?