SELECT 
  T.TABLESPACE_NAME
 ,NVL(ROUND((SELECT SUM(BYTES)/1048576 FROM DBA_SEGMENTS@TESTE S WHERE S.TABLESPACE_NAME=T.TABLESPACE_NAME),2),0) MEGAS
FROM DBA_TABLESPACES@TESTE T
WHERE NOT EXISTS
(
  SELECT 1 FROM DBA_TABLESPACES L
  WHERE L.TABLESPACE_NAME=T.TABLESPACE_NAME
)
/

WITH LOCAL AS
(
  SELECT TABLESPACE_NAME, NVL(ROUND(SUM(MAXBYTES)/1048576,2),0) MAXSIZE
  FROM DBA_DATA_FILES
  GROUP BY TABLESPACE_NAME
), REMOTO AS
(
  SELECT S.TABLESPACE_NAME, NVL(ROUND(SUM(BYTES)/1048576,2),0) SEGS
  FROM DBA_SEGMENTS@TESTE S 
  GROUP BY TABLESPACE_NAME
)
SELECT
  L.*, R.SEGS
FROM LOCAL L
LEFT JOIN REMOTO R ON (L.TABLESPACE_NAME=R.TABLESPACE_NAME )
WHERE L.MAXSIZE < R.SEGS 
/