关于SQLServer2005的学习笔记——生日问题

生日问题是个看似简单逻辑上却又比较复杂的小问题

主要的逻辑难点第一个是关于闰月尾天的计算，第二个是判断本年度生日是否已过

本文给出了三种解决办法，

第一种是最常用的解决办法，即常用的
SQL

语法，不过看起来比较复杂，适合环境为
SQLServer2000
以上

第二种是采用函数的方法，把对日期的逻辑处理放到函数中，调用起来会简约一下，适合环境为
SQLServer2000
以上

第三种是采用
CTE
的方法，用
CTE
来封装判断逻辑，适合环境为
SQLServer2005
以上

-- 创建表和数据 CREATE TABLE employees ( name VARCHAR(50), birthday DATETIME ) INSERT INTO employees VALUES('WBQ','1948-12-08'); INSERT INTO employees VALUES('CZH','1952-02-19'); INSERT INTO employees VALUES('LB','1963-08-30'); INSERT INTO employees VALUES('YLL','1937-09-19'); INSERT INTO employees VALUES('YGQ','1955-03-04'); INSERT INTO employees VALUES('CHH','1963-07-02'); INSERT INTO employees VALUES('SWG','1960-05-29'); INSERT INTO employees VALUES('HW','1958-01-01'); INSERT INTO employees VALUES('YY','1972-02-29'); INSERT INTO employees VALUES('LM','1999-02-08'); INSERT INTO employees VALUES('ZY','1972-06-09'); INSERT INTO employees VALUES('WZH','1999-02-28'); SELECT name,birthday FROM employees

-- 普通的 SQL 实现 SELECT name, birthday, GETDATE() getdate, CONVERT(VARCHAR(10),GETDATE(),120) todayVarchar, CONVERT(DATETIME,CONVERT(VARCHAR(10),GETDATE(),120)) todayDateTime, DATEDIFF(YY,birthday,GETDATE()) DateBetween, DATEADD(YY,DATEDIFF(YY,birthday,GETDATE()),birthday) ThisBirthday, DATEADD(YY,DATEDIFF(YY,birthday,GETDATE())+1,birthday) NextBirthday, CASE WHEN CONVERT(DATETIME,CONVERT(VARCHAR(10),GETDATE(),120))>DATEADD(YY,DATEDIFF(YY,birthday,GETDATE()),birthday) THEN DATEADD(YY,DATEDIFF(YY,birthday,GETDATE())+1,birthday) ELSE DATEADD(YY,DATEDIFF(YY,birthday,GETDATE()),birthday) END newBirthdayStandard, CASE WHEN CONVERT(DATETIME,CONVERT(VARCHAR(10),GETDATE(),120))>DATEADD(YY,DATEDIFF(YY,birthday,GETDATE()),birthday) THEN DATEADD(YY,DATEDIFF(YY,birthday,GETDATE())+1,birthday)+ CASE WHEN DAY(birthday)=29 AND DAY(DATEADD(YY,DATEDIFF(YY,birthday,GETDATE())+1,birthday))=28 THEN 1 ELSE 0 END ELSE DATEADD(YY,DATEDIFF(YY,birthday,GETDATE()),birthday) + CASE WHEN DAY(birthday)=29 AND DAY(DATEADD(YY,DATEDIFF(YY,birthday,GETDATE()),birthday))=28 THEN 1 ELSE 0 END END newBirthdayForeign FROM employees

-- 使用函数来实现 CREATE FUNCTION GetBirthday(@birthday DATETIME,@flag INT) RETURNS DATETIME AS BEGIN DECLARE @BirthdayRet DATETIME,@BirthdayThis DATETIME,@BirthdayNext DATETIME,@today DATETIME,@dateBetween INT SET @today=CONVERT(DATETIME,CONVERT(VARCHAR(10),GETDATE(),120)) SET @dateBetween=DATEDIFF(YY,@birthday,GETDATE()) SET @BirthdayThis=DATEADD(YY,@DateBetween,@birthday) SET @BirthdayNext=DATEADD(YY,@DateBetween+1,@birthday) IF @flag=1 --2 月 29 日的生日计算为 2 月 28 日 BEGIN IF @today>@BirthdayThis SET @BirthdayRet=@BirthdayNext ELSE SET @BirthdayRet=@BirthdayThis END ELSE --2 月 29 日的生日计算为 3 月 1 日 BEGIN IF @today>@BirthdayThis IF DAY(@birthday)=29 AND DAY(@BirthdayNext)=28 SET @BirthdayRet=@BirthdayNext+1 ELSE SET @BirthdayRet=@BirthdayNext ELSE IF DAY(@birthday)=29 AND DAY(@BirthdayThis)=28 SET @BirthdayRet=@BirthdayThis+1 ELSE SET @BirthdayRet=@BirthdayThis END RETURN @BirthdayRet END SELECT name,birthday,dbo.GetBirthday(birthday,0),dbo.GetBirthday(birthday,1) FROM employees

-- 通过 CTE 来实现 WITH DateBetween AS ( SELECT name, birthday, GETDATE() getdate, CONVERT(VARCHAR(10),GETDATE(),120) todayVarchar, CONVERT(DATETIME,CONVERT(VARCHAR(10),GETDATE(),120)) todayDateTime, DATEDIFF(YY,birthday,GETDATE()) DateBetween FROM employees ), DateBirthdayThisAndNext AS ( SELECT name,birthday,getdate,todaydatetime,datebetween, DATEADD(YY,DateBetween,birthday) AS DateCur, DATEADD(YY,DateBetween+1,birthday) AS DateNext FROM DateBetween ), DateBirthdayThisAndNextForeign AS ( SELECT name,birthday,todaydatetime, DateCur,DateNext, DateCur+CASE WHEN DAY(birthday)=29 AND DAY(DateCur)=28 THEN 1 ELSE 0 END AS DateCurForeign, DateNext+CASE WHEN DAY(birthday)=29 AND DAY(DateNext)=28 THEN 1 ELSE 0 END AS DateNextForeign FROM DateBirthdayThisAndNext ), DateBirthday AS ( SELECT name,birthday, CASE WHEN DateCurForeign>=todaydatetime THEN DateCurForeign ELSE DateNextForeign END AS birthDayForeign, CASE WHEN DateCur>=todaydatetime THEN DateCur ELSE DateNext END AS birthDayStandard FROM DateBirthdayThisAndNextForeign ) SELECT name,birthday,birthDayForeign,birthDayStandard FROM DateBirthday