Функция plpgsql с циклом по таблице change_request

create or replace function change_request() returns void as $$
DECLARE 
  r record;
BEGIN
  for r in select * from change_request loop
    execute format('ALTER TABLE %I ADD COLUMN %I %s', 
                   r.table_name, r.column_name, r.column_type);
  end loop;
END $$
language plpgsql;