-- set default
alter table tbl_name alter col_name set default 3;
alter table tbl_name alter col_name set default USER;
alter table tbl_name alter col_name set default CURRENT_USER;
alter table tbl_name alter col_name set default SESSION_USER;
alter table tbl_name alter col_name set default SYSTEM_USER;
alter table tbl_name alter col_name set default NULL;