用DATEADD减去年份不能正确处理leap年

Question

While subtracting a year form current date, if current day is February 28 2013 then below statement returns February 28 2012 , but correct result should be February 29 2012 as 2012 is a leap year. How can this scenario be handled.

SELECT DATEADD(year, -1, GETDATE())

Answer 1

* 使用此代码*

SELECT DATE_SUB('2013-02-28', INTERVAL 365 DAY)

Answer 2

Well, here's something to think about...

SELECT CASE WHEN DAY(LAST_DAY('2012-02-28'))=29 THEN 'foo' ELSE 'bar' END x;
+------+
| x    |
+------+
| foo  |
+------+
1 row in set (1.22 sec)

SELECT CASE WHEN DAY(LAST_DAY('2013-02-28'))=29 THEN 'foo' ELSE 'bar' END x;
+------+
| x    |
+------+
| bar  |
+------+

Answer 3

Using your logic you should use case to process last day of the month in different way. If today is a last day of the month it will be the last day of the month one year ago.

SELECT CASE WHEN LAST_DAY(CURDATE())=CURDATE()
            THEN LAST_DAY(DATE_SUB(CURDATE(),INTERVAL 1 YEAR)) 
            ELSE DATE_SUB(CURDATE(),INTERVAL 1 YEAR)
       END     

But what you will do if today is 29.02 ? WHAT day a year ago it should be? In this case for 28.02 and 29.02 you get the same 28.02 a year ago. What logic we should use here?