Simple query to check Database growth in GB with respect to time---
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select to_char(Trunc(creation_time,'MM'), 'MON RRRR') "Month",
sum(bytes)/1024/1024/1024 "Growth in GB"
from sys.v_$datafile
where creation_time > SYSDATE-9999
group by Trunc(creation_time,'MM')
order by Trunc(creation_time,'MM');