根据一个人的出生日期和今天的日期，计算他最近的生日（使用Northwind数据库的Employees表）

使用Northwind的Employees表，根据存储的Birthdate返回每个员工离今天最近的生日，如果今年的生日已经过了，则返回明年的，反之，则返回今年的（注意，如果是闰年2月29日出生的，则在下个月的3月1号过生日）

 

 

WITH    arg1
          AS ( SELECT   FirstName ,
                        LastName ,
                        BirthDate ,
                        DATEDIFF(YEAR, BirthDate, GETDATE()) AS DIFF ,
                        CAST(CONVERT(CHAR(8), GETDATE(), 112) AS DATETIME) AS Today
               FROM     Employees
             ),
        arg2
          AS ( SELECT   FirstName ,
                        LastName ,
                        BirthDate ,
                        DATEADD(YEAR, DIFF, BirthDate) AS CurrentBirthday ,
                        DATEADD(YEAR, DIFF + 1, BirthDate) AS NextBirthday ,
                        Today
               FROM     arg1
             ),
        arg3
          AS ( SELECT   FirstName ,
                        LastName ,
                        BirthDate ,
                        CurrentBirthday
                        + CASE WHEN DAY(BirthDate) = 29
                                    AND DAY(CurrentBirthday) = 28 THEN 1
                               ELSE 0
                          END AS CurrentBirthday ,
                        NextBirthday
                        + CASE WHEN DAY(Birthdate) = 29
                                    AND DAY(NextBirthday) = 28 THEN 1
                               ELSE 0
                          END AS NextBirthday ,
                        Today
               FROM     arg2
             )
    SELECT  FirstName ,
            LastName ,
            BirthDate ,
            CASE WHEN Today > CurrentBirthday THEN NextBirthday
                 ELSE CurrentBirthday
            END AS Birthday
    FROM    arg3