SQL - Group several lines in the same column with LIST TAG

SQL :

SELECT country, 
listagg(first_name, ', ') WITHIN GROUP (order by first_name) 
FROM tablename 
GROUP BY country

SQL v2 workaround for "too long string column concatenation" :

with PRECALC as (
   select floor(4000/(max(length(MY_COLUMN)+LENGTH(',')))) as MAX_FIELD_LENGTH
   from MY_TABLE
)

select 
    LISTAGG(MY_COLUMN,',') WITHIN GROUP(ORDER BY floor(rownum/MAX_FIELD_LENGTH), MY_COLUMN)
from MY_TABLE, PRECALC
group by floor(rownum/MAX_FIELD_LENGTH);