select username from user_users;
select table_name from user_tables;
select index_name from user_indexes;
select sequence_name from user_sequences;
select table_name,constraint_name from user_constraints;
select username from all_users;
select table_name from all_tables;
select index_name from all_indexes;
select sequence_name from all_sequences;
select table_name,constraint_name from all_constraints;