Release of space after delete/truncate table

Question

Hello,
How does release of space after delete/truncate table works? Is the space used before deletion released once delete is complete or not? Will I see the space occupied by deleted table as free in dba_segments or will I need to reorganize the table (drop and recreate again?). Reason why I am asking is that I can see table with 0 rows, but in dba_segment I can see it is occupying few gigabytes....
Thank you

Answer 1

Here is a little illustration for you;
SQL> conn ogan/password
Connected.
SQL> create table ogan_deneme as select * from all_objects;
Table created.
SQL> select count(*) from ogan_deneme;
  COUNT(*)
    228470
SQL> set line 1000
SQL> set pagesize 1000
SQL> select * from dba_segments where owner='OGAN';
OWNER    SEGMENT_NAME        PARTITION_NAME           SEGMENT_TYPE       TABLESPACE_NAME                HEADER_FILE HEADER_BLOCK      BYTES     BLOCKS    EXTENTS INITIAL_EXTENT NEXT_EXTENT MIN_EXTENTS MAX_EXTENTS PCT_INCREASE  FREELISTS FREELIST_GROUPS RELATIVE_FNO BUFFER_
OGAN      OGAN_DENEME          TABLE              SYSTEM                                 854       319981   *30408704*       *1856*         *44*          65536                       1  2147483645                       1               1          854 DEFAULT
SQL> truncate table ogan_deneme;
Table truncated.
SQL> select * from dba_segments where owner='OGAN';
OWNER    SEGMENT_NAME        PARTITION_NAME           SEGMENT_TYPE       TABLESPACE_NAME                HEADER_FILE HEADER_BLOCK      BYTES     BLOCKS    EXTENTS INITIAL_EXTENT NEXT_EXTENT MIN_EXTENTS MAX_EXTENTS PCT_INCREASE  FREELISTS FREELIST_GROUPS RELATIVE_FNO BUFFER_
OGAN      OGAN_DENEME           TABLE              SYSTEM                                 854       319981      *65536*          *4*          *1*          65536                       1  2147483645                       1               1          854 DEFAULT
SQL>Hope it Helps,
Ogan