How to find database growth on a Monthly wise

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DATABASE GROWTH ON A MONTHLY WISE
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select to_char(CREATION_TIME,'RRRR') year, to_char(CREATION_TIME,'MM') month, round(sum(bytes)/1024/1024/1024) GB
from   v$datafile
group by  to_char(CREATION_TIME,'RRRR'),   to_char(CREATION_TIME,'MM')
order by   1, 2;

YEAR MO              GB
---- -- ---------------
2011 09              74
2012 06            4579
2012 07             334
2012 08             523
2012 09             652