Oracle list all schema and tablespaces

[Nitin]

List all users/schema
         SET PAGESIZE 50
         SELECT DISTINCT USERNAME FROM DBA_USERS;
 
List ONLY your tables
         SET PAGESIZE 80
         COL TABLE__NAME FORMAT a30;
         COL TABLE_TYPE FORMAT a30;
         SELECT * FROM CAT;

List the Oracle Tablespaces and free space
         SELECT * from v$TABLESPACE;

List the free space for all Oracle Tablespaces within a Database
         SELECT * from DBD_FREE_SPACE where TABLESPACE_NAME = 'IATOR';

List the space ALREADY USED for a specific Oracle Tablespace
         SELECT * from DBA_SEGMENTS where TABLESPACE_NAME = 'myTABLESPACE';

List extents for segments
         SELECT TABLESPACE_NAME, count(*), max(blocks), sum(blocks) from dba_free_space group by TABLESPACE_name;

See all the tables you have access to:
         SET PAGESIZE 90
         COLUMN "OBJECT NAME" format a26
         COLUMN "OBJECT TYPE" format a20
         SELECT object_name    "OBJECT NAME",
                object_type    "OBJECT TYPE"
         FROM
                user_objects
         WHERE
                object_type = 'TABLE';

See your TABLESPACE
         SELECT TABLESPACE_NAME from ALL_TABLES where TABLE_NAME = '<your_table>'