Query on Shrinking Table - Oracle
I assume you have a Basicfile LOB, because shrink is not supported with Securefile LOBs. The segment is not being moved, so the default tablespace and the tablespace of the segment is not relevant now. So a simple test is:

SQL&gt; create table t1(c1 clob) lob (c1) store as basicfile;

Table created.

SQL&gt; insert into t1 select lpad('X', 4000) from dual connect by level&lt;=10000;

10000 rows created.

SQL&gt; commit;

Commit complete.

SQL&gt; select bytes/1024/1024 from user_segments where segment_name = 
     (select segment_name from user_lobs where table_name = 'T1' and column_name = 'C1');

BYTES/1024/1024
---------------
             80

SQL&gt; alter table t1 enable row movement;

Table altered.

SQL&gt; delete from t1 where rownum &lt;= 5000;

5000 rows deleted.

SQL&gt; commit;

Commit complete.

SQL&gt; alter table t1 modify lob (c1) (shrink space);

Table altered.


And the LOB segment became half the size after the shrink operation:

SQL&gt; select bytes/1024/1024 from user_segments where segment_name = 
     (select segment_name from user_lobs where table_name = 'T1' and column_name = 'C1');

BYTES/1024/1024
---------------
        39.8125