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，
-- 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
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