why i am not getting any thing when i use the command match in php and mysql

when i write this code and run the script i get no error and i get nothing but
one of my rows in d_title  --  have fsd in it
but when i search i get nothing while i need to get wow one time

$query = " SELECT d_title FROM link  
                WHERE MATCH (d_title) AGAINST ('fsd')"; 
    $res = mysql_query($query) or die(mysql_error()); 
    while ($row = mysql_fetch_array($res))
	 {
    echo "wow";
}

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