How to convert four-digit Julian (yddd) to Gregorian (mm/dd/yy, etc.) in script loader? - sql

Question

The Goal
To have the data script handle the logic and conversion to a date format that is parsable/readable by a QlikSense/QlikView line graph. AKA it needs to be a normal format. (YYYYMMDD, MM/DD/YY, etc.)
Context
All relevant tables to the date is in one table.
The field the date data is in is called "date", and is successfully referenced in Qliksheets by using [Date]
ddd is the Day of the Year. y is the last digit of the year. The decade is assumed to be 2010s, therefore we can safely add "201" before the digit, giving you the year.
Examples of four-digit Julian: 9001 is January 1st, 2019. 9283 is October 10th, 2019
What I've Tried
I've been going along the route of simply adding "201" before the first digit of the provided four-digit number, and then calculating the last/next three digits of the four-digit number.
Currently, I haven't even gotten to the calculation part, as I can't even get the string concatenation to work. All my attempts have circulated around the following:
[AwesomeSheet]:
LOAD
Right([Date], 3) as JulianDay, // Get day
Left([Date], 1) as JulianYearSingleDigit, // Get year
201 & JulianYearSingleDigit & JulianDay as TempField // Attempt to concatenate the numbers
// Here be the JulianDay calculation
Date#([TempField], 'YYYYMMDD') as FormattedDate // Format into readable format for line graph
FROM [my-awesome-file.csv];

Answer 1

Possible solution is to get the year start date, add the number of days to it and convert to date:
date(
date#( '201' & left([Date], 1) & '0101', 'YYYYMMDD')
-1
+ num( mid([Date], 2,4) )
)
What the calculation is doing:
getting the first character from the date left([Date], 1)
adds 201 to format it as year number '201' & left([Date], 1)
adds 0101 to it '201' & left([Date], 1) & '0101'
(at this point this part will be equal to 20190101 (as string))
date#( '201' & left([Date], 1) & '0101', 'YYYYMMDD') - this will "tell" Qlik that the string inside is a date in format YYYYMMDD
to the year start we'll add the days (last 3 symbols from the original string) num( mid([Date], 2,4) )
cast all to date
As a result 9283 = 10/10/2019
So your script will look like:
[AwesomeSheet]:
LOAD
date(
date#('201' & left([Date], 1) & '0101', 'YYYYMMDD')
-1
+ num( mid([Date], 2,4) )
) as FormattedDate
FROM [my-awesome-file.csv];
Thats one possible way. There might be shorter/easier way but this is on top of my head

Answer 2

It sounds like what you want is a dayOfYearToYmd converter - this might help "Convert day of year to datetime in SQL Server"
Also, these might help regarding the concept of Julian dates:
https://en.wikipedia.org/wiki/Julian_day
http://www.fourmilab.ch/documents/calendar/
Julian days simply enumerate the days and fraction which have elapsed since the start of the Julian era, which is defined as beginning at noon on Monday, 1st January of year 4713 B.C.E. in the Julian calendar.
, ie any date before the reference date has a negative value, anything after is positive, which doesn't fit with your post.
Given the above, you could declare the start of each calendar year as a reference date. :)