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)