DEFINE SUBQUERY $sub() AS
    $foo_url = "http_test://" || "foo1.txt";
    PRAGMA FILE("foo.txt", $foo_url);
    $bar_url = "http_test://" || "bar1.txt" || substring(FileContent("foo.txt"),10);
    PRAGMA FILE("bar.txt", $bar_url);
    SELECT
        $bar_url;
END DEFINE;

SELECT
    *
FROM $sub();