this is a part of my query:
group_concat(distinct(concat_ws(' ', dts.first_name, dts.last_name)) separator ', ') as data_team_specialists
I have following problem: if first_name and last_name exist everything works fine, persons are separated with ', ' and there is a space between first and last name.
But: if first_name is NULL the next person is separated with ' ' (space) from concat_ws and not with ', ' as it should