Current DateTime as a string

DECLARE @CurrentDateTime as varchar(50)

SELECT @CurrentDateTime = CAST(Year(GetDate()) as nvarchar(4)) 
+ (CASE 
WHEN Month(GetDate()) < 10 THEN '0' + CAST(Month(GetDate()) as nvarchar(2))
ELSE CAST(Month(GetDate()) as nvarchar(2))
END)
+ (CASE 
WHEN Day(GetDate()) < 10 THEN '0' + CAST(Day(GetDate()) as nvarchar(2))
ELSE CAST(Day(GetDate()) as nvarchar(2))
END)
+ '_'
+ (CASE 
WHEN DatePart(hour, GetDate()) < 10 THEN '0' + CAST(DatePart(hour, GetDate()) as nvarchar(2)) ELSE CAST(DatePart(hour, GetDate()) as nvarchar(2))
END)
+ (CASE 
WHEN DatePart(minute, GetDate()) < 10 THEN '0' + CAST(DatePart(minute, GetDate()) as nvarchar(2))
ELSE CAST(DatePart(minute, GetDate()) as nvarchar(2))
END)
+ (CASE 
WHEN DatePart(second, GetDate()) < 10 THEN '0' + CAST(DatePart(second, GetDate()) as nvarchar(2))
ELSE CAST(DatePart(second, GetDate()) as nvarchar(2))
END)

SELECT @CurrentDateTime