SELECT useragent,referer,time FROM usersinfo 
INNER JOIN
(SELECT MIN(time) AS mt, useragent FROM usersinfo GROUP BY useragent) AS t
ON usersinfo.time = t.mt AND usersinfo.useragent = t.useragent
WHERE date  = '".$date."'

SELECT useragent,referer,MIN(time) FROM usersinfo WHERE date=$date GROUP BY useragent

SELECT usersinfo.useragent, usersinfo.referer ,usersinfo.time FROM usersinfo 
INNER JOIN
(SELECT MIN(time) AS mt, useragent FROM usersinfo GROUP BY useragent) AS t
ON usersinfo.time = t.mt AND usersinfo.useragent = t.useragent
WHERE date  = '".$date."'

SELECT *
FROM (SELECT * FROM `usersinfo` WHERE `date` = '{$date}' ORDER BY `time` DESC) 
GROUP BY `useragent`

SELECT *
FROM (SELECT * FROM `usersinfo` WHERE `date` = '{$date}' ORDER BY `time` DESC) AS `tabl1`
GROUP BY `useragent`

        function read_usersinfo($date){

            $sql_usersinfo = "
            SELECT *
            FROM (SELECT useragent,ip,referer,time FROM usersinfo WHERE date = {$date} ORDER BY time DESC) 
            GROUP BY useragent" ;
            
            if(!$date){
                die("error");
            }
            
            $res = $this->sql($sql_usersinfo) ;
            
            while($row = mysql_fetch_array($res)){               
              $data[] = $row;
            }
            
            return $data;
        }


        $counter = read_usersinfo('2012-04-07') ;
        
        echo "<pre>" ;
        print_r($counter);
        echo "</pre>" ;