$x = (SELECT * FROM (VALUES (1)) AS x(a));
$y = (SELECT * FROM (VALUES (1)) AS y(b));
$z = (SELECT * FROM (VALUES (1)) AS z(c));

SELECT * FROM $x WHERE a IN (
    SELECT b FROM $y AS y JOIN $z AS z ON (y.b == z.c)
    UNION ALL
    SELECT b FROM $y AS y JOIN $z AS z ON (y.b == z.c)
);