do {
    let rs = try database.executeQuery("select x, y, z from test", values: nil)
    while rs.next() {
        if let x = rs.string(forColumn: "x"), let y = rs.string(forColumn: "y"), let z = rs.string(forColumn: "z") {
            print("x = (x); y = (y); z = (z)")
        }
    }
} catch {
    print("error: (error.localizedDescription)")
}