Handle error for duplicate entries - PHP MySQL

Question

I have a PHP form which enters data into my MySQL database. My primary key is one of the user-entered values. When the user enters a value that already exists in the table,

Answer 1

You can check the return value from mysql_query when you do the insert.

$result = mysql_query("INSERT INTO mytable VALUES ('dupe')");

if (!$result) {
    echo "Enter a different value";
} else {
    echo "Save successful.";
}