Grouping repeated fields in BQ

Question

I have the following table where "product" is a repeated field.

How can I group by "id" and merge the repeated field to sum the quantities so the output looks like this.

Trying to find an elegant solution that does not unnest.

Answer 1

Consider below

select id, array(
  select as struct sku, sum(quantity) quantity
  from t.product
  group by sku
  ) product
from (
  select id, array_concat_agg(product) product
  from your_table
  group by id
) t          

if applied to sample data in your question - output is