not allowing the same row of data to be inserted in a mysql table

[BJansen]

suppose you have site that users can submit their names to participate in some classes.the users will fill a form,then hit submit,and their names and telephone numbers will go to a table in a mysql database.the thing I want to do is that I want to prevent a user to submit his/her name twice by checking if the phone numbers are the same(I know it is silly this way,but I am just saying as an example).so what should I do?I am using this method to insert the form data into the data base:\[code\] $pdo = new PDO('mysql:host=localhost;dbname=form', 'formuser', 'password'); $fname = $_REQUEST['fname']; //first name from the form $lname = $_REQUEST['lname']; //last name from the form $pnumber = $_REQUEST['pnumber'] //phone number from the form $query = 'INSERT INTO list SET firstname = "' . $fname . '", lastname = "' . $lname . '", phonenumber ="' . $pnumber . '", date = CURDATE()'; $pdo->exec($query);\[/code\]And I know this is not a safe way to insert data into the database.again I am trying to figure out a way and then deploy better solutions for submitting the data.