Format DateTime as yyyy-MM-dd
You want ISO8601 formats in SQL Server, here you go.
In SQL Server 2014 forward you can do this...
select Format(GetDate(), 'yyyy-MM-dd HH:mm:ss.ffffff')
I'm not sure exactly when that came into existence. Here's the older techniques, which were maddening...
For yyyy-MM-dd :
CONVERT(VARCHAR(10), GetDate(), 120)
e.g.
select CONVERT(VARCHAR(10), GetDate(), 120)
2017-02-02
Format "120" is 24-hour time, down to the second. But we limit the size of the result to remove the time component.
To include the time component just use a varchar that is 19 or more characters long, e.g. 50
select CONVERT(VARCHAR(50), GetDate(), 120)
2017-02-02 11:09:53
Or for the ever useful sortable reporting month: yyyy-MM
Select CONVERT(VARCHAR(7), GetDate(), 120)
2017-02
To get milliseconds (and 24 hour time) use format "121" -- it extends 120 by including the milliseconds.
Select CONVERT(VARCHAR(23), GetDate(), 121)
2017-02-02 11:52:33.980
(Any length 23 or larger will suffice)