show all databases sqlplus

11) To view database
2
3select * from v$database;
4
52) To view instance
6
7select * from v$instance;
8
93) To view all users
10
11select * from all_users;
12
13
144) To view table and columns for a particular user
15
16select tc.table_name Table_name
17,tc.column_id Column_id
18,lower(tc.column_name) Column_name
19,lower(tc.data_type) Data_type
20,nvl(tc.data_precision,tc.data_length) Length
21,lower(tc.data_scale) Data_scale
22,tc.nullable nullable
23FROM all_tab_columns tc
24,all_tables t
25WHERE tc.table_name = t.table_name;