dbtest=> create table zakaznik (kodZak char(5) primary key, Firma CHAR(40) NOT NULL);
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "zakaznik_pkey" for table "zakaznik"

dbtest=> create table objednavka (cisloObj serial primary key, zakaznik char(5) references zakaznik(kodZak), mezisoucet dec(17,2));
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "objednavka_pkey" for table "objednavka"
CREATE TABLE

dbtest=> insert into zakaznik values ('AAAAA', 'Kočička');
INSERT 28854 1

dbtest=> insert into objednavka (zakaznik,mezisoucet)values ('BBBBB', 150.50);
ERROR:  insert or update on table "objednavka" violates foreign key constraint "$1"
DETAIL:  Key (zakaznik)=(BBBBB) is not present in table "zakaznik".¨

dbtest=> insert into objednavka (zakaznik,mezisoucet)values ('AAAAA', 150.50);
INSERT 28891 1

dbtest=> select * from objednavka;
 cisloobj | zakaznik | mezisoucet
----------+----------+------------
        1 | AAAAA    |     150.50
(1 row)


dbtest=> create table rozpisObj (cisloVyr int not null, cislObj int references objednavka(cisloObj), pocetKs smallint, sleva smallint check (sleva between 0 and 100));
CREATE TABLE

dbtest=> insert into rozpisObj values (5489, 1, 15, 101);
ERROR:  new row for relation "rozpisobj" violates check constraint "rozpisobj_sleva"

dbtest=> insert into rozpisObj values (5489, 1, 15, 50);
INSERT 28892 1

dbtest=> insert into rozpisObj values (null, 1, 15, 50);
ERROR:  null value in column "cislovyr" violates not-null constraint