如何在 sql 中创建动态列？

Question

有一个 table，日期列格式为数字 (20150101)。我如何计算每个月有多少天，并在新的临时 table 中创建月份作为列。例如，如果我有：

Date
20150101
20150102
20150201
20150302
20150304

我愿意return

Jan  Feb   Mar
2    1     2

谢谢

Answer 1

试试这个：

DECLARE @t TABLE ( d INT )
INSERT  INTO @t
VALUES  ( 20150101 ),
        ( 20150102 ),
        ( 20150201 ),
        ( 20150302 ),
        ( 20150304 );
WITH    cte
          AS ( SELECT   LEFT(DATENAME(mm,
                                      ( CAST(CAST(d AS NVARCHAR(8)) AS DATE) )),
                             3) AS m ,
                        COUNT(*) AS c
               FROM     @t
               GROUP BY LEFT(DATENAME(mm,
                                      ( CAST(CAST(d AS NVARCHAR(8)) AS DATE) )),
                             3)
             )
    SELECT  *
    FROM    cte PIVOT ( MAX(c) FOR m IN ( [Jan], [Feb], [Mar], [Apr], [May],
                                          [Jun], [Jul], [Aug], [Sep], [Oct],
                                          [Nov], [Dec] ) ) AS p

输出：

Jan Feb Mar Apr     May     Jun     Jul     Aug     Sep     Oct     Nov     Dec
2   1   2   NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL    NULL

只计算不同的日期：

DECLARE @t TABLE ( d INT )
INSERT  INTO @t
VALUES  ( 20150101 ),
        ( 20150101 ),
        ( 20150102 ),
        ( 20150201 ),
        ( 20150302 ),
        ( 20150304 );
WITH    cte
          AS ( SELECT   LEFT(DATENAME(mm,
                                      ( CAST(CAST(d AS NVARCHAR(8)) AS DATE) )),
                             3) AS m ,
                        COUNT(*) AS c
               FROM    (SELECT DISTINCT * FROM @t) t
               GROUP BY LEFT(DATENAME(mm,
                                      ( CAST(CAST(d AS NVARCHAR(8)) AS DATE) )),
                             3)
             )
    SELECT  *
    FROM    cte PIVOT ( MAX(c) FOR m IN ( [Jan], [Feb], [Mar], [Apr], [May],
                                          [Jun], [Jul], [Aug], [Sep], [Oct],
                                          [Nov], [Dec] ) ) AS p