求日期所属星座的 TSQL UDF (用户自定义函数)

use northwind
go
create function udf_GetStar (@ datetime)
returns varchar(100)
-- 返回日期所属星座,如果有静态的 星座对照码表 直接在查询中 join 效率相对更高
begin
return
(
--declare @ datetime
--set @ = getdate()
select max(star)
from
(
select '魔羯座' as star,1 as [month],1 as [day]
union all select '水瓶座',1,20
union all select '双鱼座',2,19
union all select '牡羊座',3,21
union all select '金牛座',4,20
union all select '双子座',5,21
union all select '巨蟹座',6,22
union all select '狮子座',7,23
union all select '处女座',8,23
union all select '天秤座',9,23
union all select '天蝎座',10,24
union all select '射手座',11,22
union all select '魔羯座',12,22
) stars
where [month] * 40 + [day]
=
(
select max([month] * 40 + [day])
from (
select '魔羯座' as star,1 as [month],1 as [day]
union all select '水瓶座',1,20
union all select '双鱼座',2,19
union all select '牡羊座',3,21
union all select '金牛座',4,20
union all select '双子座',5,21
union all select '巨蟹座',6,22
union all select '狮子座',7,23
union all select '处女座',8,23
union all select '天秤座',9,23
union all select '天蝎座',10,24
union all select '射手座',11,22
union all select '魔羯座',12,22
) stars
where [month] * 40 + [day] <= month(@) * 40 + day(@)
)
)
end
go
CREATE FUNCTION GetStar1(@ datetime)
RETURNS varchar(100)
AS
BEGIN
--仅一句 SQL 搞定
--如果有静态的 星座对照码表 直接在查询中 join 效率相对更高
RETURN
(
--declare @ datetime
--set @ = getdate()
select max(star)
from
(
-- 星座,该星座开始日期所属月,该星座开始日期所属日
select '魔羯座' as star,1 as [month],1 as [day]
union all select '水瓶座',1,20
union all select '双鱼座',2,19
union all select '牧羊座',3,21
union all select '金牛座',4,20
union all select '双子座',5,21
union all select '巨蟹座',6,22
union all select '狮子座',7,23
union all select '处女座',8,23
union all select '天秤座',9,23
union all select '天蝎座',10,24
union all select '射手座',11,22
union all select '魔羯座',12,22
) stars
where dateadd(day,[day]-1,dateadd(month,[month]-1,dateadd(year,datediff(year,0,@),0)))
=
(
select max(dateadd(day,[day]-1,dateadd(month,[month]-1,dateadd(year,datediff(year,0,@),0))))
from
(
select '魔羯座' as star,1 as [month],1 as [day]
union all select '水瓶座',1,20
union all select '双鱼座',2,19
union all select '牧羊座',3,21
union all select '金牛座',4,20
union all select '双子座',5,21
union all select '巨蟹座',6,22
union all select '狮子座',7,23
union all select '处女座',8,23
union all select '天秤座',9,23
union all select '天蝎座',10,24
union all select '射手座',11,22
union all select '魔羯座',12,22
) stars
where @ >= dateadd(day,[day]-1,dateadd(month,[month]-1,dateadd(year,datediff(year,0,@),0)))
)
)
end

go

declare @ datetime
set @ = getdate()

select *
from stars
where [month] * 40 + [day] =
(
select max(stars.[month] * 40 + stars.[day])
from stars
where stars.[month] * 40 + stars.[day] <= month(@) * 40 + day(@)
)

go
select c.birthdate,a.star
from employees c
left join stars a
on month(c.birthdate) * 40 + day(c.birthdate) >= a.month * 40 + a.day
left join stars b
on a.month * 40 + a.day < b.month * 40 + b.day
and b.month * 40 + b.day  = (select min(month * 40 + day) from stars where month * 40 + day > a.month * 40 + a.day)
where month(c.birthdate) * 40 + day(c.birthdate) < isnull(b.month * 40 + b.day,999)

select *
from stars a
left join stars b
on a.month * 40 + a.day < b.month * 40 + b.day
and b.month * 40 + b.day  = (select min(month * 40 + day) from stars where month * 40 + day > a.month * 40 + a.day)

select a.birthdate,b.star,dbo.udf_getstar1(a.birthdate),dbo.udf_getstar(a.birthdate)
from employees a
left join
(
select a.*,isnull(b.month,12) as m,isnull(b.day,31) as d
from stars a
left join stars b
on a.month * 40 + a.day < b.month * 40 + b.day
and b.month * 40 + b.day  = (select min(month * 40 + day) from stars where month * 40 + day > a.month * 40 + a.day)
) b
on month(a.birthdate) * 40 + day(a.birthdate) >= b.month * 40 +  b.day
and month(a.birthdate) * 40 + day(a.birthdate) < b.m * 40 +  b.d

select e.birthdate,a.star
from employees e
left join stars a
on month(e.birthdate) * 40 + day(e.birthdate) >= a.month * 40 + a.day
left join stars b
on a.month * 40 + a.day < b.month * 40 + b.day
and b.month * 40 + b.day  = (select min(month * 40 + day) from stars where month * 40 + day > a.month * 40 + a.day)
where month(e.birthdate) * 40 + day(e.birthdate) < isnull(b.month * 40 + b.day,999)
go


--测试
use northwind
select dbo.getstar(birthdate),count(*)
from employees
group by dbo.getstar(birthdate)

create  function Weekday(@Date datetime)
returns integer
begin
--1: Monday , ... ,7: Sunday
return (select (@@datefirst + datepart(weekday,@Date)) % 7
        + case when (@@datefirst + datepart(weekday,@Date)) % 7 < 2
                    then 6
               else -1
          end)
end