'schetin', 'CREATE TABLE `schetin` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `date_create` datetime DEFAULT NULL,
  PRIMARY KEY (`id`),
) ENGINE=InnoDB AUTO_INCREMENT=29 DEFAULT CHARSET=utf8'

'rko', 'CREATE TABLE `rko` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `id_schetin` int(10) unsigned DEFAULT NULL,
  `id_prihodnakl` int(10) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `FK1B956D686371A` (`id_schetin`),
  KEY `FK1B956E9FE512` (`id_prihodnakl`),
  CONSTRAINT `FK_RKO_5_id_schetin` FOREIGN KEY (`id_schetin`) REFERENCES `schetin` (`id`) ON DELETE SET NULL ON UPDATE NO ACTION,
  CONSTRAINT `FK_RKO_6_id_prihodnakl` FOREIGN KEY (`id_prihodnakl`) REFERENCES `prihodnakl` (`id`) ON DELETE SET NULL,
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8'

'prihodnakl', 'CREATE TABLE `prihodnakl` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `date_create` datetime DEFAULT NULL,
  `summa` double DEFAULT NULL,
  `id_schetin` int(10) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `FKC29CFB8AD686371A` (`id_schetin`),
  CONSTRAINT `FK_prihodnakl_7` FOREIGN KEY (`id_schetin`) REFERENCES `schetin` (`id`) ON DELETE SET NULL,
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8'

SELECT s.id as idSchetin, p.id as idPrihodNakl, r.id as idRKO FROM schetin s
left join (rko r, prihodnakl p)
on (s.id=p.id_schetin and p.id=r.id_prihodnakl)
order by p.id;

SELECT s.id as idSchetin, p.id as idPrihodNakl, r.id as idRKO FROM schetin s
left join (rko r, prihodnakl p)
on (s.id=p.id_schetin and p.id=r.id_prihodnakl)
order by p.id;

select 
	a.id as id_schetin,
	b.id as id_prihodnakl,
	c.id as id_rko
from schetin a 
left join prihodnakl b on a.id=b.id_schetin
left join rko c on (a.id=c.id_schetin or b.id=c.id_prihodnakl)