USE longtbspace-name
...
    If USE longtbspace-name is specified, USE tbspace-name must also be specified. If it is not, the longtbspace-name argument is ignored.

reorg MYTABLE allow no access use tmp32 longlobdata

CALL REORGCHK_TB_STATS('S', 'SYSIBM');

SELECT 
CASE 
  WHEN S.DATATYPE = 'A' AND T.AVGROWSIZE * 255 < (S.PAGESIZE - 68) THEN (ST.CARD / 255 + 1) * (S.PAGESIZE - 68)
  ELSE ST.TSIZE
END AS TSIZE
, ST.TABLE_SCHEMA, ST.TABLE_NAME
FROM SESSION.TB_STATS ST
JOIN SYSCAT.DATAPARTITIONS P ON P.TABSCHEMA = ST.TABLE_SCHEMA AND P.TABNAME = ST.TABLE_NAME AND P.SEQNO = 0
JOIN SYSCAT.TABLESPACES S ON S.TBSPACEID = P.TBSPACEID
JOIN SYSCAT.TABLES T ON T.TABSCHEMA = ST.TABLE_SCHEMA AND T.TABNAME = ST.TABLE_NAME
WHERE ST.DATAPARTITIONNAME = '' 
;