Difference between dba_segments and dba_users when trying to identify list of schema in Oracle DB

Question

I am trying to figure out the list schema created in a database, I came across many answers like this and this which are trying to tell either use dba_segments or use dba_users .

But when I use those in my database then results have substantial difference.

I am looking for answers explaining which one is correct ( dba_segments or dba_users ) and why, so please do not think that my question is "how to get a list of all available schema in database".

Answer 1

dba_segments shows SEGMENTS - which are owned by schemas

you can have a schema that has no segments - objects that use segments can generally be thought of as tables or indexes. A user could own a synonym or a PL/SQL unit but have no segments for example.

Here's a list of segment types for my 12c system

HR@orcl🍻🍺 >select distinct segment_type from dba_segments;


SEGMENT_TYPE     
LOBINDEX         
INDEX PARTITION  
ROLLBACK         
NESTED TABLE     
TABLE PARTITION  
LOB PARTITION    
LOBSEGMENT       
INDEX            
TABLE            
CLUSTER  

dba_users will show you EVERY user in the database, whether they own 'data' or not

here's how to find SCHEMAS with no segments, or one way

HR@orcl🍻🍺 >select distinct username
  2  from dba_users
  3  minus
  4  select distinct owner
  5  from dba_segments;


USERNAME               
ANONYMOUS              
APEX_LISTENER          
APEX_PUBLIC_USER       
APEX_REST_PUBLIC_USER  
APPQOSSYS              
BASIC_PRIVS            
BI...