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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
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-- 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),120)) todayDateTime,
? DATEDIFF(YY,birthday,GETDATE()) DateBetween,
? DATEADD(YY,DATEDIFF(YY,GETDATE()),birthday) ThisBirthday,GETDATE())+1,birthday) NextBirthday,
? CASE WHEN CONVERT(DATETIME,120))>DATEADD(YY,birthday)
?????? THEN DATEADD(YY,birthday)
?????? ELSE DATEADD(YY,birthday)
? END newBirthdayStandard,birthday)???????
?????? THEN DATEADD(YY,birthday)+
??????????? CASE WHEN DAY(birthday)=29 AND DAY(DATEADD(YY,birthday))=28 THEN 1 ELSE 0 END
?????? ELSE DATEADD(YY,birthday) +
??????????? CASE WHEN DAY(birthday)=29 AND DAY(DATEADD(YY,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,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,dbo.GetBirthday(birthday,0),1) FROM employees
?
-- 通过 CTE 来实现
WITH DateBetween AS
(
? SELECT??
??? name,
?? ? birthday,
??? GETDATE() getdate,
??? CONVERT(VARCHAR(10),
??? CONVERT(DATETIME,
??? DATEDIFF(YY,GETDATE()) DateBetween
? FROM employees
),
DateBirthdayThisAndNext AS
(
? SELECT
??? name,getdate,todaydatetime,datebetween,
??? DATEADD(YY,DateBetween,birthday) AS DateCur,DateBetween+1,birthday) AS DateNext
? FROM DateBetween
),
DateBirthdayThisAndNextForeign AS
(
? SELECT
??? name,
??? 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,
??? 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,birthDayForeign,birthDayStandard FROM DateBirthday
（编辑：李大同）
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