Historical Tablespace Usages

select  thedate,  gbsize,  prev_gbsize,  gbsize-prev_gbsize diff from        (  select  thedate,  gbsize,  lag(gbsize,1) over (order by r) prev_gbsize  from    (  select  rownum r,  thedate,  gbsize  from    (  select  trunc(thedate) thedate,  max(gbsize) gbsize  from    (  select  to_date(to_char(snapshot.begin_interval_time,'YYYY-MON-DD HH24:MI:SS'),'YYYY-MON-DD HH24:MI:SS') thedate,  round((usage.tablespace_usedsize*block_size.value)/1024/1024/1024,2) gbsize  from    dba_hist_tbspc_space_usage usage,  v$tablespace               tablespace,  dba_hist_snapshot          snapshot,  v$parameter                block_size  where   usage.snap_id       = snapshot.snap_id  and     usage.tablespace_id = tablespace.ts#  and     tablespace.name     = '&tablespace'  and     block_size.name     = 'db_block_size'  )  group by  trunc(thedate)  order by  trunc(thedate)  )  )  );