INSERT... ON DUPLICATE KEY UPDATE issue - php

Question

I am having a mysql table named company_profile. It may have only one record. So I tried to insert and update data of the table using INSERT.... ON DUPLICATE KEY UPDATE query.
This is how I tried it:
$sql = "INSERT INTO company_profile (
company_name
, tel
, mobile
, fax
, email
) VALUES (?, ?, ?, ?, ?)
ON DUPLICATE KEY UPDATE
company_name= VALUES(company_name)
, tel = VALUES(tel)
, mobile = VALUES(mobile)
, fax = VALUES(fax)
, email = VALUES(email)";
$stmt = $mysqli->prepare($sql);
$stmt->bind_param('sssss', $company_name
, $telephone
, $mobile
, $fax
, $email
);
$stmt->execute();
My problem is when I updating the data, it always inserting a new record into my table.
Can anybody tell me what would be the problem of this?
My table structure looks like this:
CREATE TABLE IF NOT EXISTS company_profile (
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
company_name VARCHAR(120) NOT NULL,
tel VARCHAR(20) NOT NULL,
mobile VARCHAR(20) NOT NULL,
fax VARCHAR(20) DEFAULT NULL,
email VARCHAR(60) NOT NULL,
PRIMARY KEY (id),
UNIQUE KEY (id)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

Answer 1

First, it is redundant to define a key as being both unique and primary key. Just define id to be primary key.
Then, you need a unique constraint/index on the columns used for duplication (the two are functionally equivalent for this purpose). I am guessing uniqueness is based on the company name:
create unique index unq_company_profile_company_name on company_profile(company_name);