Help with populating table

[lingo5]

Hello, I have 2 MySQL tables, one is for Companies and the other for Users.

 

The primary key for both is the field id_E.

 

Both tables have the fields id_E and E_nombre, this one being the company name.

 

I have created a PHP script to add a new user to the DB which contains a select menu. This menu shows a list of companies from the companies table and sends the company id (id_E) to the users table to create a new user.

 

My problem is that I would like the DB to automatically populate the E_nombre field on the Users table with the content of the E_nombre field of the companies table based on the id_E sent to the users table by the create new user form.

 

This is the query I use to create a new user.

 

if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {
  $insertSQL = sprintf("INSERT INTO t_usuarios (id_E, usuarionombre, usuariologin, usuariopassword) VALUES (%s, %s, %s, %s)",
                       GetSQLValueString($_POST['id_E'], "int"),
				   GetSQLValueString($_POST['usuarionombre'], "text"),
                       GetSQLValueString($_POST['usuariologin'], "text"),
                       GetSQLValueString($_POST['usuariopassword'], "text"));
                       //GetSQLValueString($_POST['usuariolastvisit'], "date"));

  mysql_select_db($database_amat_connect, $amat_connect);
  $Result1 = mysql_query($insertSQL, $amat_connect) or die(mysql_error());
}

 

I hope I have explained properly. Thanks for your help.