Alternatives of array_agg() or string_agg() on redshift

Redshift has a listagg function you can use instead:

SELECT _bs, LISTAGG(_wbns, ',') FROM bag GROUP BY _bs;

To get an array type back instead of a varchar, you need to combine the LISTAGG function with the SPLIT_TO_ARRAY function like so:

SELECT
  some_grouping_key,
  SPLIT_TO_ARRAY(LISTAGG(col_to_agg, ','), ',')
FROM some_table
GROUP BY 1

you have to use listagg for reshift

For each group in a query, the LISTAGG aggregate function orders the rows for that group according to the ORDER BY expression, then concatenates the values into a single string.

LISTAGG is a compute-node only function. The function returns an error if the query doesn't reference a user-defined table or Amazon Redshift system table.

Your query will be as like below

select _bs, 
listagg(_wbns,',')
within group (order by _wbns) as val
from bag
group by _bs
order by _bs;

for better understanding Listagg

Use listagg function:

select _bs, 
listagg(_wbns,',')
within group (order by _bs) as val
from bag
group by _bs