Checking for duplicates in MySql db

[webnewone]

Very new to all of this so please be gentle! I have the following code below but need to know what to add to it to check for duplicates in the "prospects" firld?

Much appreciate any help!

<?php
$user = "######";
$pass = "#######";
$db = "########";
$link = mysql_connect( "localhost", $user, $pass );
if ( ! $link )
die("Couldn't connect to MySQL" );
mysql_select_db( $db, $link )
or die ( "Couldn't open $db: ".mysql_error() );
$query = "INSERT INTO prospects ( id, address )
VALUES('', '$address')";
mysql_query( $query, $link )
or die("Database INSERT Error");
?>

[TTT]

make other check query

$q1 = mysql_query(select id from prospects
where address = '$address');

if(mysql_num_rows > 0)
{
echo "row already exists";
}
else
{
... do other query
}