Converting JDE Julian date to Gregorian

Question

I'm trying to convert JDE dates, and have amassed a large quantity of information and figured I'd try to do an SQL conversion function to simplify some tasks.

Here's the function I came up with, which I simply call "ToGregorian"

CREATE FUNCTION [dbo].[ToGregorian](@julian varchar(6))
RETURNS datetime AS BEGIN
    DECLARE @datetime datetime

    SET @datetime = CAST(19+CAST(SUBSTRING(@julian, 1, 1) as int) as varchar(4))+SUBSTRING(@julian, 2,2)+'-01-01'
    SET @datetime = DATEADD(day, CAST(SUBSTRING(@julian, 4,3) as int)-1, @datetime)

    RETURN @datetime
END

1. Takes a "julian" string.
2. Takes the first letter and adds it to century, starting from 19th.
3. Adds decade and years from the next 2 characters.
4. Finally adds the days, which are the final 3 characters, and subtracts 1 as it already had 1 day in the first setup. (eg. 2011-01-01)
5. Result ex: 111186 => 2011-07-05 00:00:00.000

In my opinion this is a bit clumsy and overkill, and I'm hoping there is a better way of doing this. Perhaps I'm doing too many conversions or maybe I should use a different method alltogether?

Any advice how to improve the function?
Perhaps a different, better, method?
Wouldn't mind if it could be more readable as well...

I've also got an inline version, where if for instance, I only have read privileges and can't use functions, which also looks messy, is it possible to make it more readable, or better?

CAST(REPLACE(Convert(VARCHAR, DATEADD(d,CAST(SUBSTRING(CAST([column] AS VARCHAR), 4,3) AS INT)-1, CAST(CAST(19+CAST(SUBSTRING(CAST([column] AS VARCHAR), 1,1) AS INT) AS VARCHAR)+SUBSTRING(CAST([column] AS VARCHAR), 2,2) + '-01-01' AS DATETIME)), 111), '/', '-') AS DATETIME)

Answer 1

The accepted answer is incorrect. It will fail to give the correct answer for 116060 which should be 29th February 2016. Instead it returns 1st March 2016.

JDE seems to store dates as integers, so rather than converting from strings I always go direct from the integer:

DATEADD(DAY, @Julian % 1000, DATEADD(YEAR, @Julian / 1000, '31-dec-1899'))

To go from a varchar(6) I use:

DATEADD(DAY, CAST(RIGHT(@Julian,3) AS int), DATEADD(YEAR, CAST(LEFT(@Julian,LEN(@Julian)-3) AS int), '31-dec-1899'))