DROP DATABASE IF EXISTS mnoziny;
CREATE DATABASE IF NOT EXISTS mnoziny;
USE mnoziny;

CREATE TABLE a (x INT, y VARCHAR(5));
CREATE TABLE b (x INT, y VARCHAR(5)); 

INSERT INTO a(x,y) VALUES(1,'A');
INSERT INTO a(x,y) VALUES(2,'B');
INSERT INTO a(x,y) VALUES(3,'C');
INSERT INTO a(x,y) VALUES(4,'D');
INSERT INTO b(x,y) VALUES(1,'A');
INSERT INTO b(x,y) VALUES(3,'C');
INSERT INTO b(x,y) VALUES(5,'E');
INSERT INTO b(x,y) VALUES(60, NULL);