datediff()

Question

 SELECT DATEDIFF(YEAR,'2010-4-10','2013-4-10') AS DiffDate  --3岁是正确的
  SELECT DATEDIFF(YEAR,'2010-4-10','2012-4-9') AS DiffDate  -- 结果是2，但实际还差一天满2岁呀，怎么得到正确的年龄呀第二个参数是生日，第三个参数是当前日期。我想通过datediff()算出儿童几岁了，该如何算呀

Answer 1

SELECT DATEDIFF(YEAR,'2010-4-10','2013-4-10') + case when DATEDIFF(DAY,DATEADD(YEAR,DATEDIFF(YEAR,'2010-4-10','2012-4-9') ,'2010-4-10'),'2013-4-10') < 0 then -1 else 0 end
AS DiffDate 
SELECT DATEDIFF(YEAR,'2010-4-10','2012-4-9') + case when DATEDIFF(DAY,DATEADD(YEAR,DATEDIFF(YEAR,'2010-4-10','2012-4-9') ,'2010-4-10'),'2012-4-9') < 0 then -1 else 0 end
AS DiffDate

Answer 2

儿童一般算周，直接SELECT DATEDIFF(WEEK ,'2010-4-10','2013-4-10') AS Diffweek
SELECT DATEDIFF(WEEK ,'2010-4-10','2012-4-9') 
AS Diffweek