select distinct segment_type from dba_segments可以得到当前所有使用的segment_type
系统中还有哪些没有被使用的segment_type
通过select text from dba_views where view_name = 'DBA_SEGMENTS'可以得出dba_segments的视图定义
select owner, segment_name, partition_name, segment_type, tablespace_name,
       header_file, header_block,
       decode(bitand(segment_flags, 131072), 131072, blocks,
           (decode(bitand(segment_flags,1),1,
            dbms_space_admin.segment_number_blocks(tablespace_id, relative_fno,
            header_block, segment_type_id, buffer_pool_id, segment_flags,
            segment_objd, blocks), blocks)))*blocksize,
       decode(bitand(segment_flags, 131072), 131072, blocks,
           (decode(bitand(segment_flags,1),1,
            dbms_space_admin.segment_number_blocks(tablespace_id, relative_fno,
            header_block, segment_type_id, buffer_pool_id, segment_flags,
            segment_objd, blocks), blocks))),
       decode(bitand(segment_flags, 131072), 131072, extents,
           (decode(bitand(segment_flags,1),1,
           dbms_space_admin.segment_number_extents(tablespace_id, relative_fno,
           header_block, segment_type_id, buffer_pool_id, segment_flags,
           segment_objd, extents) , extents))),
       initial_extent, next_extent, min_extents, max_extents, pct_increase,
       freelists, freelist_groups, relative_fno,
       decode(buffer_pool_id, 0, 'DEFAULT', 1, 'KEEP', 2, 'RECYCLE', NULL)
from sys_dba_segs

sys_dba_segs又是什么
通过select object_type from dba_objects where object_name = upper('sys_dba_segs')可以得出sys_dba_segs是一个视图

继续查询
select text from dba_views where view_name = upper('sys_dba_segs')可以得到
select NVL(u.name, 'SYS'), o.name, o.subname,
       so.object_type, s.type#,
       ts.ts#, ts.name, ts.blocksize,
       f.file#, s.block#,
       s.blocks * ts.blocksize, s.blocks, s.extents,
       s.iniexts * ts.blocksize,
       decode(bitand(ts.flags, 3), 1, to_number(NULL),
                                      s.extsize * ts.blocksize),
       s.minexts, s.maxexts,
       decode(bitand(ts.flags, 3), 1, to_number(NULL),
                                      s.extpct),
       decode(bitand(ts.flags, 32), 32, to_number(NULL),
              decode(s.lists, 0, 1, s.lists)),
       decode(bitand(ts.flags, 32), 32, to_number(NULL),
              decode(s.groups, 0, 1, s.groups)),
       s.file#, s.cachehint, NVL(s.spare1,0), o.dataobj#
from sys.user$ u, sys.obj$ o, sys.ts$ ts, sys.sys_objects so, sys.seg$ s,
     sys.file$ f
where s.file# = so.header_file
  and s.block# = so.header_block
  and s.ts# = so.ts_number
  and s.ts# = ts.ts#
  and o.obj# = so.object_id
  and o.owner# = u.user# (+)
  and s.type# = so.segment_type_id
  and o.type# = so.object_type_id
  and s.ts# = f.ts#
  and s.file# = f.relfile#
union all
select NVL(u.name, 'SYS'), un.name, NULL,
       decode(s.type#, 1, 'ROLLBACK', 10, 'TYPE2 UNDO'), s.type#,
       ts.ts#, ts.name, ts.blocksize, f.file#, s.block#,
       s.blocks * ts.blocksize, s.blocks, s.extents,
       s.iniexts * ts.blocksize, s.extsize * ts.blocksize, s.minexts,
       s.maxexts, s.extpct,
       decode(bitand(ts.flags, 32), 32, to_number(NULL),
         decode(s.lists, 0, 1, s.lists)),
       decode(bitand(ts.flags, 32), 32, to_number(NULL),
         decode(s.groups, 0, 1, s.groups)),
       s.file#, s.cachehint, NVL(s.spare1,0), un.us#
from sys.user$ u, sys.ts$ ts, sys.undo$ un, sys.seg$ s, sys.file$ f
where s.file# = un.file#
  and s.block# = un.block#
  and s.ts# = un.ts#
  and s.ts# = ts.ts#
  and s.user# = u.user# (+)
  and s.type# in (1, 10)
  and un.status$ != 1
  and un.ts# = f.ts#
  and un.file# = f.relfile#
union all
select NVL(u.name, 'SYS'), to_char(f.file#) || '.' || to_char(s.block#), NULL,
       decode(s.type#, 2, 'DEFERRED ROLLBACK', 3, 'TEMPORARY',
                      4, 'CACHE', 9, 'SPACE HEADER', 'UNDEFINED'), s.type#,
       ts.ts#, ts.name, ts.blocksize,
       f.file#, s.block#,
       s.blocks * ts.blocksize, s.blocks, s.extents,
       s.iniexts * ts.blocksize,
       decode(bitand(ts.flags, 3), 1, to_number(NULL),
                                      s.extsize * ts.blocksize),
       s.minexts, s.maxexts,
       decode(bitand(ts.flags, 3), 1, to_number(NULL),
                                      s.extpct),
       decode(bitand(ts.flags, 32), 32, to_number(NULL),
         decode(s.lists, 0, 1, s.lists)),
       decode(bitand(ts.flags, 32), 32, to_number(NULL),
         decode(s.groups, 0, 1, s.groups)),
       s.file#, s.cachehint, NVL(s.spare1,0), s.hwmincr
from sys.user$ u, sys.ts$ ts, sys.seg$ s, sys.file$ f
where s.ts# = ts.ts#
  and s.user# = u.user# (+)
  and s.type# not in (1, 5, 6, 8, 10)
  and s.ts# = f.ts#
  and s.file# = f.relfile#

即segment_type包括包括ROLLBACK,TYPE2 UNDO,DEFERRED ROLLBACK,TEMPORARY,CACHE,SPACE HEADER,UNDEFINED和sys_objects里面的object_type

通过select distinct object_type from sys_objects可以得到sys_objects里面所有的object_type，在此不一一列举

其实sys_objects也是一个view,在dba_views可以获知其定义

注意测试环境oracle database 10.2.0.1