Oracle 18c

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CREATE TABLE t (id NUMBER, x XMLTYPE)
  XMLTYPE x STORE AS BASICFILE BINARY XML (DISABLE STORAGE IN ROW RETENTION NONE)
  ENABLE ROW MOVEMENT;
INSERT INTO t SELECT object_id, XMLTYPE('<z>' || object_name || '</z>') FROM all_objects WHERE rownum <= 1000;
1000 rows affected

COMMIT;
UPDATE T SET x=NULL;
1000 rows affected

COMMIT;
SELECT l.column_name, segment_name, s.bytes/1024/1024 as mb 
  FROM user_lobs l
  JOIN user_segments s using (segment_name);


COLUMN_NAME
SEGMENT_NAME
MB


SYS_NC00003$
SYS_LOB0000125058C00003$$
9


SELECT * FROM user_tab_columns WHERE table_name = 'T';


TABLE_NAME
COLUMN_NAME
DATA_TYPE
DATA_TYPE_MOD
DATA_TYPE_OWNER
DATA_LENGTH
DATA_PRECISION
DATA_SCALE
NULLABLE
COLUMN_ID
DEFAULT_LENGTH
DATA_DEFAULT
NUM_DISTINCT
LOW_VALUE
HIGH_VALUE
DENSITY
NUM_NULLS
NUM_BUCKETS
LAST_ANALYZED
SAMPLE_SIZE
CHARACTER_SET_NAME
CHAR_COL_DECL_LENGTH
GLOBAL_STATS
USER_STATS
AVG_COL_LEN
CHAR_LENGTH
CHAR_USED
V80_FMT_IMAGE
DATA_UPGRADED
HISTOGRAM
DEFAULT_ON_NULL
IDENTITY_COLUMN
EVALUATION_EDITION
UNUSABLE_BEFORE
UNUSABLE_BEGINNING
COLLATION


T
ID
NUMBER
null
null
22
null
null
Y
1
null
null
null
0x
0x
null
null
null
null
null
null
null
NO
NO
null
0
null
NO
YES
NONE
NO
NO
null
null
null
null

T
X
XMLTYPE
null
SYS
2000
null
null
Y
2
null
null
null
0x
0x
null
null
null
null
null
null
null
NO
NO
null
0
null
NO
YES
NONE
NO
NO
null
null
null
null


select table_name, column_name, data_type 
from user_tab_cols 
where 
  table_name = 'T' and hidden_column = 'YES'
  and
  column_id = (
      select column_id 
      from user_tab_cols 
      where table_name = 'T' and column_name = 'X'
  ) 


TABLE_NAME
COLUMN_NAME
DATA_TYPE


T
SYS_NC00003$
BLOB


--ALTER TABLE t MODIFY LOB (x) (SHRINK SPACE);
ORA-00900: invalid SQL statement

DECLARE
  l_name USER_TAB_COLUMNS.COLUMN_NAME%TYPE;
  l_stmt VARCHAR2(100);
BEGIN
  select column_name
  into l_name
  from user_tab_cols 
  where 
    table_name = 'T' and hidden_column = 'YES'
    and
    column_id = (
        select column_id 
        from user_tab_cols 
        where table_name = 'T' and column_name = 'X'
    );

--  SELECT segment_name
--  INTO l_name
--  FROM user_lobs l 
--  JOIN user_segments s using (segment_name);

  l_stmt := 'ALTER TABLE t MODIFY LOB ("' || l_name || '") (SHRINK SPACE)';
  dbms_output.put_line(l_stmt);
  execute immediate l_stmt;
END;
/
1 rows affected

dbms_output:
ALTER TABLE t MODIFY LOB ("SYS_NC00003$") (SHRINK SPACE)

SELECT l.column_name, segment_name, s.bytes/1024/1024 as mb 
  FROM user_lobs l 
  JOIN user_segments s using (segment_name);


COLUMN_NAME
SEGMENT_NAME
MB


SYS_NC00003$
SYS_LOB0000125058C00003$$
.0625


drop table t purge;

TABLE_NAME	COLUMN_NAME	DATA_TYPE	DATA_TYPE_MOD	DATA_TYPE_OWNER	DATA_LENGTH	DATA_PRECISION	DATA_SCALE	NULLABLE	COLUMN_ID	DEFAULT_LENGTH	DATA_DEFAULT	NUM_DISTINCT	LOW_VALUE	HIGH_VALUE	DENSITY	NUM_NULLS	NUM_BUCKETS	LAST_ANALYZED	SAMPLE_SIZE	CHARACTER_SET_NAME	CHAR_COL_DECL_LENGTH	GLOBAL_STATS	USER_STATS	AVG_COL_LEN	CHAR_LENGTH	CHAR_USED	V80_FMT_IMAGE	DATA_UPGRADED	HISTOGRAM	DEFAULT_ON_NULL	IDENTITY_COLUMN	EVALUATION_EDITION	UNUSABLE_BEFORE	UNUSABLE_BEGINNING	COLLATION
T	ID	NUMBER	null	null	22	null	null	Y	1	null	null	null	0x	0x	null	null	null	null	null	null	null	NO	NO	null	0	null	NO	YES	NONE	NO	NO	null	null	null	null
T	X	XMLTYPE	null	SYS	2000	null	null	Y	2	null	null	null	0x	0x	null	null	null	null	null	null	null	NO	NO	null	0	null	NO	YES	NONE	NO	NO	null	null	null	null