实时根据每月天数取数据每日数据

SELECT  top (datediff(day, dateadd(month, datediff(month, 0, getdate()), 0), dateadd(month, datediff(month, 0, dateadd(month, 1, getdate())), -1)) + 1)
    CONVERT(date, dateadd(month, datediff(month, 0, getdate()), 0)) AS 本月第一天,
    CONVERT(date, dateadd(month, datediff(month, 0, dateadd(month, 1, getdate())), -1)) AS 本月最后一天,
    datediff(day, dateadd(month, datediff(month, 0, getdate()), 0), dateadd(month, datediff(month, 0, dateadd(month, 1, getdate())), -1)) + 1 AS 本月天数,
    name,
    value 
FROM
    [dbo].[OPC_VFDaily] UNPIVOT (
        value FOR name IN ( Day1, Day2, Day3, Day4, Day5, Day6, Day7, Day8, Day9, Day10, Day11, Day12,Day13,Day14,Day15,Day16,Day17,Day18,Day19,Day20,Day21,Day22,Day23,Day24,Day25,Day26,Day27,Day28,Day29,Day30,Day31) 
    ) AS UnpivotedData