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COLUMN TABLE_NAME FORMAT A32
COLUMN OBJECT_NAME FORMAT A32
COLUMN OWNER FORMAT A10
 
SELECT
   owner, TABLE_NAME, TRUNC(SUM(bytes)/1024/1024) Meg
FROM
(SELECT segment_name TABLE_NAME, owner, bytes
 FROM dba_segments
 WHERE segment_type = 'TABLE'
 UNION ALL
 SELECT i.TABLE_NAME, i.owner, s.bytes
 FROM dba_indexes i, dba_segments s
 WHERE s.segment_name = i.index_name
 AND   s.owner = i.owner
 AND   s.segment_type = 'INDEX'
 UNION ALL
 SELECT l.TABLE_NAME, l.owner, s.bytes
 FROM dba_lobs l, dba_segments s
 WHERE s.segment_name = l.segment_name
 AND   s.owner = l.owner
 AND   s.segment_type = 'LOBSEGMENT'
 UNION ALL
 SELECT l.TABLE_NAME, l.owner, s.bytes
 FROM dba_lobs l, dba_segments s
 WHERE s.segment_name = l.index_name
 AND   s.owner = l.owner
 AND   s.segment_type = 'LOBINDEX')
WHERE owner IN UPPER('&owner')
GROUP BY TABLE_NAME, owner
HAVING SUM(bytes)/1024/1024 > 10  /* Ignore really small tables */
ORDER BY SUM(bytes) DESC
;