Add a unique key to database - php

Question

I've got a form on my website for users to input their fname, sname, company,phone,email which then gets updated to a database on submit. I also have a field in my database for a unique userID to incase users have same name and company ect. When submitting my form how is it possible to add in this field, a unique number so that it is +1 from the fields taken already. At the minute there are only 3 userIDs so i need the next inputted one to be 4 and so on.
At the moment I have this.
require_once('dbConnect.php');
//taken from a smarty template form.
$addForename = $_POST['forename'];
$addSurname = $_POST['surname'];
$addCompany = $_POST['company'];
$addContact = $_POST['contact'];
$addEmail = $_POST['email'];
public function addUser($addForename,$addSurname,$addCompany,$addContact,$addEmail)
{
$sql = "INSERT INTO `Users` (`Forename`, `Surname`, `ComanyName`, `Phone`, `Email`) VALUES ('".$addForename."','".$addSurname."','".$addCompany."','".$addContact."','".$addEmail."')";
$databaseAccess = new DatabaseConnect();
try
{
$result = $databaseAccess->connect($sql, "add");
}
catch (Exception $e)
{
throw new Exception("Adding User Failed !!!");
}
if ($result)
{
return 1;
}
else{return 0;}
}
thanks

Answer 1

If you are using phpmyadmin there should be a checkbox when youre creating a new column with "A_I" or Auto_Increment.. you have to check that and then it will count your entrys.

Answer 2

Create the row as an auto_increment in the database:
create table someName (ID int primary key auto_increment, col1 int ...);
Then when you are inserting data, either pass it a null, or don't insert that field like this:
insert into someName (col1) values (3);
or
insert into someName (ID, col1) values (null, 3);
You can modify your current table with the following:
ALTER TABLE someName MODIFY COLUMN ID INT NOT NULL AUTO_INCREMENT , ADD PRIMARY KEY (ID);

Answer 3

create the ID:
ALTER TABLE users ADD ID INT UNSIGNED
NOT NULL AUTO_INCREMENT, ADD PRIMARY KEY (ID);
and start the auto-increment where you want
ALTER TABLE tbl AUTO_INCREMENT = 4;

Answer 4

Create a column set it as a primary key and auto increment. You can even write a stored procedure for inserting in the table. That way you don't have to write query every time and not have to worry about escape characters. If you want the particular no to be returned from stored procedure use SCOPE_IDENTITY() in the stored procedure.