Can you tell me why this isn't working? If the viewer has the same ip as one in the database it still adds it again

PHP Code:

$ip = $_SERVER['REMOTE_ADDR'];
$result = mysql_query("SELECT * FROM `unique_hits` WHERE `ip`=`$ip`");
if (!$result) mysql_query("INSERT INTO `unique_hits` (`ID` , `ip`) VALUES ('', '$ip')");
$unique_sql_hits = mysql_query("SELECT * FROM `unique_hits`");
$unique_hits = mysql_num_rows($unique_sql_hits); 


Surely $result will only be false if the query failed? An empty result set is still a result.

Instead of if(!$result), try if(mysql_num_rows($result) == 0)

Oberon already found the bug
I just want to share one more thing.
Normally, I'll set 'ID' field as auto_increment so we don't have to put it into MySql queries.