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select
age_in_months(Now(), '1988-06-21'), --calculates completed period without current month
age_in_years(Now(), '1988-06-21'), --calculates completed period without current month
datediff('month', '1988-06-21', Now()) as MonthsBetweenDates, --includes current month in calculation
datediff('year', '1988-06-21', Now()) as YearsBetweenDates, --includes current month in calculation
months_between (Now(),'2017-01-01') -- calculates months between two dates as a float
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select
period_diff(201712, 201707) as Past, --months between now and a past date
period_diff(201806, 201712) as Future --months between now and a future date