mysql - Prevent duplicate records to a table using PHP

Question

I want to prevent duplicate values into a database table from a form using PHP.

I have created the following:

A database with a table named clients:

CREATE TABLE clients(
 firstName varchar(20),
 lastName varchar(20),
 primary key(firstName, lastName));

A simple form named form.html

<h2>Enter your First and Last Name</h2>
<form action="frm_script.php" method="post">
<p><strong>First Name:</strong><br /> <input type="text" name="firstName" /></p>
<p><strong>Last Name:</strong><br /> <input type="text" name="lastName"/></p>
<input type="submit" name="submit" value="Add Customer" />
</form>

A form processing script named frm_script.php

<?php
if(isset($_POST['submit']))
{

//get the name and comment entered by user
$firstName = $_POST['firstName'];
$lastName = $_POST['lastName'];

//connect to the database
$dbc = mysqli_connect('host', 'username', 'password', 'dbname') or die('Error connecting to MySQL server');

//insert results from the form input
$query = "INSERT IGNORE INTO clients(firstName, lastName) VALUES('$firstName', '$lastName')";

$result = mysqli_query($dbc, $query) or die('Error querying database.');

mysqli_close($dbc);
}
echo "Customer Added";
?>

So far with my frm_script.php file the above works and for a unique record displays customer added. However, for a duplicate record it throws "Error Querying Database".

How can I update the frm_script.php script for the following?

If a duplicate row is found on entering a First / Last name combination it should display the message "Client already listed" along with that record.

If no duplicate row is found on entering a First / Last name combination on the form it should insert the entry to the database and display the message "customer added"

I have read that a SELECT should be run first then an INSERT but I am not sure how to implement this into my existing code.

Answer 1

  <?php
    if(isset($_POST['submit'])) {

    //get the name and comment entered by user
    $firstName = $_POST['firstName'];
    $lastName = $_POST['lastName'];

    //connect to the database
    $dbc = mysqli_connect('host', 'username', 'password', 'dbname') or die('Error connecting to MySQL server');
    $check=mysqli_query($dbc,"select * from clients where firstname='$firstname' and lastname='$lastname'");
    $checkrows=mysqli_num_rows($check);

   if($checkrows>0) {
      echo "customer exists";
   } else {  
    //insert results from the form input
      $query = "INSERT IGNORE INTO clients(firstName, lastName) VALUES('$firstName', '$lastName')";

      $result = mysqli_query($dbc, $query) or die('Error querying database.');

      mysqli_close($dbc);
    }
    echo "Customer Added";
    };
  ?>

just check for rows in your db for firstname and lastname if exists echo- your message else insert