Queries to Check System

Check database version:

SELECT * FROM v$version;

Check directories:

SELECT file_name, tablespace_name 
FROM dba_data_files;

Check total currently data usage size:

SELECT SUM(bytes) / 1024 / 1024 AS size_in_mb
FROM dba_data_files;

Check total currently temp usage size:

SELECT SUM(bytes) / 1024 / 1024 AS temp_size_in_mb
FROM dba_temp_files;

Number of CPUs:

SELECT value AS processor_count
FROM v$osstat
WHERE stat_name = 'NUM_CPUS';