Can I Use a Nested GROUP in FOREACH?

[唐亮]

Hi group,
Can I use a nested group in foreach?

For example:

A = load data ... as (a1:..., a2:..., a3:..., ...)
B = group A by a1;

C = foreach B {
 * inner_group = group A by a2;*
  generate group, inner_group;
}

As the emphasized sentence,
can I group the inner bag again from relation B?

But the compiler complained 'group' is an invalid alias in 'inner_group' of
relation C.

So, can I or how can I use a nested group in foreach?

Thanks!!