sql server query for datediff

1-- DOES NOT ACCOUNT FOR LEAP YEARS
2DECLARE @date1 DATETIME, @date2 DATETIME, @result VARCHAR(100);
3DECLARE @years INT, @months INT, @days INT,
4    @hours INT, @minutes INT, @seconds INT, @milliseconds INT;
5
6SET @date1 = '1900-01-01 00:00:00.000'
7SET @date2 = '2018-12-12 07:08:01.123'
8
9SELECT @years = DATEDIFF(yy, @date1, @date2)
10IF DATEADD(yy, -@years, @date2) < @date1 
11SELECT @years = @years-1
12SET @date2 = DATEADD(yy, -@years, @date2)
13
14SELECT @months = DATEDIFF(mm, @date1, @date2)
15IF DATEADD(mm, -@months, @date2) < @date1 
16SELECT @months=@months-1
17SET @date2= DATEADD(mm, -@months, @date2)
18
19SELECT @days=DATEDIFF(dd, @date1, @date2)
20IF DATEADD(dd, -@days, @date2) < @date1 
21SELECT @days=@days-1
22SET @date2= DATEADD(dd, -@days, @date2)
23
24SELECT @hours=DATEDIFF(hh, @date1, @date2)
25IF DATEADD(hh, -@hours, @date2) < @date1 
26SELECT @hours=@hours-1
27SET @date2= DATEADD(hh, -@hours, @date2)
28
29SELECT @minutes=DATEDIFF(mi, @date1, @date2)
30IF DATEADD(mi, -@minutes, @date2) < @date1 
31SELECT @minutes=@minutes-1
32SET @date2= DATEADD(mi, -@minutes, @date2)
33
34SELECT @seconds=DATEDIFF(s, @date1, @date2)
35IF DATEADD(s, -@seconds, @date2) < @date1 
36SELECT @seconds=@seconds-1
37SET @date2= DATEADD(s, -@seconds, @date2)
38
39SELECT @milliseconds=DATEDIFF(ms, @date1, @date2)
40
41SELECT @result= ISNULL(CAST(NULLIF(@years,0) AS VARCHAR(10)) + ' years,','')
42     + ISNULL(' ' + CAST(NULLIF(@months,0) AS VARCHAR(10)) + ' months,','')    
43     + ISNULL(' ' + CAST(NULLIF(@days,0) AS VARCHAR(10)) + ' days,','')
44     + ISNULL(' ' + CAST(NULLIF(@hours,0) AS VARCHAR(10)) + ' hours,','')
45     + ISNULL(' ' + CAST(@minutes AS VARCHAR(10)) + ' minutes and','')
46     + ISNULL(' ' + CAST(@seconds AS VARCHAR(10)) 
47     + CASE
48            WHEN @milliseconds > 0
49                THEN '.' + CAST(@milliseconds AS VARCHAR(10)) 
50            ELSE ''
51       END 
52     + ' seconds','')
53
54SELECT @result
55