求日期所属星座的 T-SQL UDF (用户自定义函数)

use northwind
go
CREATE FUNCTION GetStar(@ datetime)
RETURNS varchar(100)
AS
BEGIN
--仅一句 SQL 搞定
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
--测试
use northwind
select dbo.getstar(birthdate),count(*)
from employees
group by dbo.getstar(birthdate)