CREATE TABLE t1 (
        a INTEGER,
        b CHARACTER
);

CREATE TABLE t2 (
        b CHARACTER,
        c INTEGER
);

INSERT INTO t1 VALUES (1,'X');
INSERT INTO t1 VALUES (2,'X');
INSERT INTO t1 VALUES (3,'Y');
INSERT INTO t1 VALUES (4,null);
INSERT INTO t1 VALUES (5,'W');

INSERT INTO t2 VALUES ('X',10);
INSERT INTO t2 VALUES ('Y',20);
INSERT INTO t2 VALUES ('Z',30);
