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select
table_name,
round((blocks*8192)/1024/1024,2) "size (Mo)" ,
round((num_rows*avg_row_len/1024/1024),2) "actual_data (Mo)",
(round((blocks*8192)/1024/1024,2) - round((num_rows*avg_row_len/1024/1024),2)) "wasted_space (Mo)"
from dba_tables
where (round((blocks*8192)/1024/1024,2) > round((num_rows*avg_row_len/1024/1024),2))
and owner not in ('SYS','SYSTEM')
and blocks != 0
order by 4 asc ;