public static Field p(String fieldName) {
        return SELECT_ALL_FROM_SOURCES_ALL.where(fieldName);
    }
@Test
    void basic_group_syntax() {
        /*
        example from vespa document:
        https://docs.vespa.ai/en/grouping.html
        all( group(a) max(5) each(output(count())
            all(max(1) each(output(summary())))
            all(group(b) each(output(count())
                all(max(1) each(output(summary())))
                all(group(c) each(output(count())
                    all(max(1) each(output(summary())))))))) );
         */
        String q = Q.p("f1").contains("v1")
                .group(
                        G.all(G.group("a"), G.maxRtn(5), G.each(G.output(G.count()),
                                G.all(G.maxRtn(1), G.each(G.output(G.summary()))),
                                G.all(G.group("b"), G.each(G.output(G.count()),
                                        G.all(G.maxRtn(1), G.each(G.output(G.summary()))),
                                        G.all(G.group("c"), G.each(G.output(G.count()),
                                                G.all(G.maxRtn(1), G.each(G.output(G.summary())))
                                        ))
                                ))
                        ))
                )
                .build();

        assertEquals(q, "yql=select * from sources * where f1 contains \"v1\" | all(group(a) max(5) each(output(count()) all(max(1) each(output(summary()))) all(group(b) each(output(count()) all(max(1) each(output(summary()))) all(group(c) each(output(count()) all(max(1) each(output(summary())))))))))");
    }