složitější select v mysql - zdvojený výpis údajů

select cat.nazev as nazev,max(UNIX_TIMESTAMP(datum)) as posledni,pp.precteno as prectene,count(udp.id) as pocet, cat.id as id  
from mgr_oboryPredmety  cat
left join predmetyStudenti ps on cat.id=ps.id_predmet 
left join diskusePrispevky udp on cat.id=udp.id_diskuse
left join diskusePrecteno pp on cat.id=pp.id_diskuse
where ps.id_student='5' and cat.semestr='1' group by udp.id order by (cat.nazev='Ostatni') ASC,cat.nazev

CREATE TABLE `diskusePrecteno` (
  `id_ctenar` smallint(6) NOT NULL,
  `id_diskuse` smallint(6) NOT NULL,
  `precteno` smallint(6) NOT NULL,
  `cas` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
) ENGINE=MyISAM DEFAULT CHARSET=latin2 COLLATE=latin2_czech_cs;


CREATE TABLE `diskusePrispevky` (
  `id` smallint(6) NOT NULL AUTO_INCREMENT,
  `id_diskuse` smallint(6) DEFAULT NULL,
  `reakce` smallint(6) DEFAULT NULL,
  `id_autora` smallint(6) NOT NULL,
  `prispevek` text COLLATE utf8_czech_ci NOT NULL,
  `datum` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
  `zobrazit` enum('ano','ne') COLLATE utf8_czech_ci NOT NULL,
  `mailem` enum('ano','ne') COLLATE utf8_czech_ci NOT NULL,
  `test` enum('ano','ne') COLLATE utf8_czech_ci NOT NULL DEFAULT 'ne',
  PRIMARY KEY (`id`),
  KEY `datum` (`datum`),
  FULLTEXT KEY `prispevek` (`prispevek`)
) ENGINE=MyISAM AUTO_INCREMENT=2727 DEFAULT CHARSET=utf8 COLLATE=utf8_czech_ci;


CREATE TABLE `oboryPredmety` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `nazev` text COLLATE utf8_czech_ci NOT NULL,
  `semestr` enum('1','2','3','4') COLLATE utf8_czech_ci NOT NULL,
  `povinne` enum('ano','ne') COLLATE utf8_czech_ci NOT NULL DEFAULT 'ano',
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=15 DEFAULT CHARSET=utf8 COLLATE=utf8_czech_ci;


CREATE TABLE `predmetyStudenti` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `id_student` int(11) NOT NULL,
  `id_predmet` int(11) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=20 DEFAULT CHARSET=utf8 COLLATE=utf8_czech_ci;