do $$
declare
selectrow record;
begin
for selectrow in
select
'ALTER TABLE '|| T.mytable || ' ADD COLUMN IF NOT EXISTS insert_by bigint' as script
from
(
select tablename as mytable from pg_tables where schemaname ='public' --your schema name here
) t
loop
execute selectrow.script;
end loop;
end;
$$;
PostgreSQL: How to add a column in every table of a database?
