具有非基值的数据透视表 [英] Pivot table with non-cardinal values

问题描述

我有一张看起来像的桌子

I have a table that looks like

Test   Reader    Result
1      John      1.6
1      Jack      5.2
2      Ursula    2.5
3      Albert    3.0
2      Jack      5.1

而且我知道每个测试最多可以有 3 个 Readers 所以我想创建一个看起来像的表格

And I know each test can have a maximum of 3 Readers so I want to create a table that looks like

Test    Reader_1 Result_1 Reader_2 Result_2 Reader_3 Result_3
1       John     1.6      Jack     5.2      (null)   (null)
2       Ursula   2.5      Jack     5.1      (null)   (null)
3       Albert   3.0      (null)   (null)   (null)   (null)

我环顾四周，似乎需要使用 PIVOT 表.唯一的问题是我找到了使用序数变量创建列的示例.在这种情况下，我有预定义数量的可能列 (3).有什么想法吗?

I looked around and it seems I need to use a PIVOT table. The only problem is that I found examples where an ordinal variable is used to create the columns. In this case case I have a predefined number of possible columns (3). Any ideas?

推荐答案

不需要多次自连接的解决方案:

A solution that does not require multiple self-joins:

您可以对 ROW_NUMBER() 分析函数的结果进行 PIVOT 以获得所需的输出:

You can PIVOT on the result of the ROW_NUMBER() analytic function to get your desired output:

SELECT *
FROM   (
  SELECT t.*,
         ROW_NUMBER() OVER ( PARTITION BY test ORDER BY ROWNUM ) AS rn
  FROM   your_table t
)
PIVOT ( MAX( Reader ) AS reader, MAX( result ) AS result FOR rn IN ( 1, 2, 3 ) );

输出:

TEST 1_READER 1_RESULT 2_READER 2_RESULT 3_READER 3_RESULT
---- -------- -------- -------- -------- -------- --------
   1 John          1.6 Jack          5.2
   2 Ursula        2.5 Jack          5.1
   3 Albert        3.0

或者，只使用聚合函数:

Or, just using aggregation functions:

SELECT test,
       MAX( CASE rn WHEN 1 THEN reader END ) AS reader_1,
       MAX( CASE rn WHEN 1 THEN result END ) AS result_1,
       MAX( CASE rn WHEN 2 THEN reader END ) AS reader_2,
       MAX( CASE rn WHEN 2 THEN result END ) AS result_2,
       MAX( CASE rn WHEN 3 THEN reader END ) AS reader_3,
       MAX( CASE rn WHEN 3 THEN result END ) AS result_3
FROM   (
  SELECT t.*,
         ROW_NUMBER() OVER ( PARTITION BY test ORDER BY ROWNUM ) AS rn
  FROM   your_table t
)
GROUP BY test;

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