Convert day of year to datetime in SQL Server

Question

In a database table (SQL Server 2012), I have dates saved in the yyyyxxx format, where xxx is the day of the year. For example 2015-08-11

Answer 1

Get the Year part, convert to datetime + add days

DECLARE @var NVARCHAR(100) = '2015223';

SELECT CAST(LEFT(@var, 4) AS DATETIME) +  CAST(RIGHT(@var, 3) AS INT) - 1;

Or:

DECLARE @var NVARCHAR(100) = '2015223';

SELECT DATEADD(dd,CAST(RIGHT(@var, 3) AS INT)-1, CAST(LEFT(@var, 4) AS DATETIME))

Or if yyyyxxx is INT:

DECLARE @var INT = 2015223;

SELECT DATEADD(dd,(@var%1000)-1, CAST(CAST((@var/1000) AS NVARCHAR(100)) 
               AS DATETIME));

LiveDemo