Oracle common SQL

1. View servers IP

select UTL_INADDR.get_host_address() from dual;

2. Current session host IP

select sys_context('USERENV', 'IP_ADDRESS') from dual

3. Server hostname

SELECT host_name from v$instance;

4. Current session hostname

select sys_context('USERENV', 'HOST') from dual;

 5. Query server platform information

SELECT * FROM DBA_REGISTRY_DATABASE;

6. Query the memory size of the server

SELECT value / 1024 / 1024 / 1024 G
  FROM v$osstat
 where stat_name = 'PHYSICAL_MEMORY_BYTES'

7. View control information

select name from v$controlfile;

8. View data files

select file_name from dba_data_files;

9. view log file

select member from v$logfile;

10. View temporary files

select file_name from Dba_temp_files;

11. see archive log

select name from v$archived_log

12. Query current user

show user

13. Query all tables of the current user

select unique tname from col;
-- perhaps 
select * from user_tables;
-- perhaps 
select * from tab;

14. Check the database creation time

SELECT TO_CHAR(CREATED, 'YYYY-MM-DD,HH24:MI:SS'), LOG_MODE FROM V$DATABASE;

15. View data objects

select owner, object_type, status, count(*) count#
  from all_objects
 group by owner, object_type, status;

16. Check the number of connections for different users

select username, count(username)
  from v$session
 where username is not null
 group by username;