我想用日期时间升序来选择不同的数字作为列。

Question

有一桌

1001  vsp,science,BBA  25-05-2020
1001  vsp,Maths,Btech  26-05-2020
1001  vsp,Maths,Btech  27-05-2020
1002  hyd,science,BBA  24-05-2020
1002  blr,Maths,Btech  25-05-2020

我想

1001  vsp,science,bba   vsp,Maths,Btech    vsp,Maths,Btech 

Answer 1

你需要一个我最喜欢的组合来实现你的目标。

• CTE（创建适当的子请求）。https:/docs.microsoft.comen-ussqlt-sqlquerieswith-commontable-expression-transact-sql。
• ROW_NUMBER（对你的行进行排序）。https:/docs.microsoft.comen-ussqlt-sqlfunctionsrow-number-transact-sql。
• PIVOT（对结果进行透视）。https:/docs.microsoft.comen-ussqlt-sqlqueriesfrom-using-pivot andunpivot。

而现在的解决方案。

WITH orderedCourse AS
(
    SELECT  GroupId,
            CourseLabel,
            ROW_NUMBER() OVER (PARTITION BY GroupId ORDER BY CourseDate) AS CourseNumber
    FROM @myCourses
)
SELECT TOP (1) GroupId, [1], [2], [3], [4]
FROM    
        (
            SELECT  GroupId,
                    CourseLabel,
                    CourseNumber
            FROM orderedCourse
        ) AS src
        PIVOT
        (
            MIN(CourseLabel) -- default agregate
            FOR CourseNumber IN ([1], [2], [3], [4] /*... if you have more courses by group*/)
        ) AS pvt
ORDER BY GroupId

给出结果。

1001  vsp,science,BBA  vsp,Maths,Btech  vsp,Maths,Btech  NULL

我用这段代码来声明这个表

INSERT INTO @myCourses
SELECT 1001, 'vsp,science,BBA', CAST('25-05-2020' AS date) UNION ALL
SELECT 1001, 'vsp,Maths,Btech', CAST('26-05-2020' AS date) UNION ALL
SELECT 1001, 'vsp,Maths,Btech', CAST('27-05-2020' AS date) UNION ALL
SELECT 1002, 'yd,science,BBA', CAST('24-05-2020' AS date) UNION ALL
SELECT 1002, 'blr,Maths,Btech', CAST('25-05-2020' AS date);

SELECT  GroupId,
        CourseLabel,
        CourseDate,
        ROW_NUMBER() OVER (PARTITION BY GroupId ORDER BY CourseDate) AS CourseNumber
FROM @myCourses;

Answer 2

只要用条件聚合与 row_number():

select col1,
       max(case when seqnum = 1 then col2 end),
       max(case when seqnum = 2 then col2 end),
       max(case when seqnum = 3 then col2 end)
from (select t.*,
             row_number() over (partition by col1 order by col3) as seqnum
      from t
     ) t
group by col1;

这与字符串聚合无关。 它也不需要大量的子查询和CTE。