create table t (n number);
-- comment on a table
SQL> comment on table t is 'this is a test table';
-- comment on a column table
SQL> comment on column t.n is 'this is number test col';
SQL> column comments format a60
SQL> select table_name, comments from user_tab_comments where table_name = 'T';
T this is a test table
SQL> select table_name, column_name, comments from user_col_comments where table_name = 'T';
T N this is number test col