[Wranglers] Stream / changefeed that only emits columns that have changed in a record.

[Ali, Saqib]

Hi,

I am looking for a way to design a stream that ONLY emits columns that
have changed in a record. If I use the stream, it emits the entire
record even if only one of the column values has changed in that
record.

Source table is as following:

create or replace table web_users (user_id int, name string, state string);
insert into web_users values (1, 'saqib', 'CA');
insert into web_users values (2, 'ali', 'AZ');

update web_users set state = 'MN' where user_id = 1;      -- sample update

One approach is that I unpivot (transpose) this data into Key Values
as following and build a stream on it:

create or replace view users_pivoted as (
  select *
  from web_users
  unpivot include nulls (kv for k in (name,  state))
);

create or replace stream users_pivoted_stream on view users_pivoted;

But I get the following error:

Change tracking is not supported on queries with 'UNPIVOT_CLAUSE'.

Any other way I can emit changes at the column level?