Question

i have a html page in which i enter data which then submits and inserts in a database on a php page. how would i validate in php that the data received is not a duplicate of the data in the database?

any help appreciated.

Answer 1

Let’s say you want to check if entered username already exists. You can do it with usual SELECT query:

$name = mysql_real_escape_string($_POST['name']);
$sql = "SELECT * FROM table WHERE name = '$name'";
$res = mysql_query($query, $connection);
if (mysql_num_rows($res) > 0 ) $error = "User already exists.";

It would be also a good idea to have your form in the php file, not html one. So, you’ll be able to show it back with all fields filled with entered data – great usability improvement