Update/insert

[jlsports]

I want to insert and or update data into a data-base. If the data already exsits I want to update the data with the new information. If the data does no exsist then I want to INSERT the data. I can't quite figure out how to accomplish this. I am sure this is probably simple. Any help would be greatly appreciated.

Thanks

[LordShryku]

$sql = "SELECT *
        FROM   table
        WHERE  unique_field = 'something'";

$res = mysql_query($sql);

if(mysql_num_rows($res)>0) {
   $ui = "UPDATE table 
          SET    blah = 'blah'
          WHERE  unique_field = 'something'";
}
else {
   $ui = "INSERT INTO table (unique_field)
          VALUES ('something')";
}
mysql_query($ui);