Convert decimal year to date

Question

I have dates in a table that are stored as decimal years. An example is 2003.024658 which translates to January 9, 2003. I would like to convert the decimal years to Oracle's date format.

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I've found someone who's done this in Excel: Decimal year to date formula?

 =DATE(INT(B1),1,MOD(B1,1)*(DATE(INT(B1)+1,1,1)-DATE(INT(B1),1,1)))

However, I can't quite figure out how to convert the logic to Oracle PL/SQL.

Answer 1

If you start from the assumption that the decimal portion was calculated according to the number of days in the given year (i.e. 365 or 366 depending on whether it was a leap year), you could do something like this:

with
 q1 as (select 2003.024658 d from dual)
,q2 as (select d
              ,mod(d,1) as decimal_portion
              ,to_date(to_char(d,'0000')||'0101','YYYYMMDD')
               as jan01
        from q1)
,q3 as (select q2.*
              ,add_months(jan01,12)-jan01 as days_in_year
        from q2)
select d
      ,decimal_portion * days_in_year as days
      ,jan01 + (decimal_portion * days_in_year) as result
from   q3;

d: 2003.024658
days: 9.00017
result: 10-JAN-2003 12:00am