如何将列结果转换为 SQL 中的列 headers？

Question

我有以下 tables:

Sample
  id PK

Test
  id PK
  name varchar

Section
  id PK
  name varchar


TestSection
  id PK
  test_id FK
  section_id FK

SampleTestResult
  id PK
  sample_id FK
  test_section_id FK
  result

当我执行以下查询时：

  SELECT DISTINCT
   s.id as sample_id, ts.name as test, str.result
  FROM sample s 
  JOIN sample_test_result str ON s.id=str.sample_id
  JOIN test_section ts ON str.test_section_id=ts.id
  JOIN section sec ON ts.section_id=sec.id

我得到一个 table，看起来像这样：

| sample_id | test       | result    |
--------------------------------------
|    1      |  t1        |   fail    |
|    1      |  t2        |   pos     |      
|    2      |  t1        |   neg     |
|    2      |  t3        |   rpt     |
|    3      |  t2        |   pos     |
|    3      |  t4        |   pos     |

不过我想以这样的 table 结束：

| sample_id | t1    | t2    | t3    | t4    |
--------------------------------------------
|    1      | fail  | pos   | NULL  | NULL  |
|    2      | neg   | NULL  | rpt   | NULL  |
|    3      | NULL  | pos   | NULL  | pos   |

如何转置 SQL 中的 table - 这在查询中可行吗？还是必须是 sql 视图？

Answer 1

使用MySQL，解决这个问题的典型方法是使用条件聚合 :

SELECT 
    s.id as sample_id,  
    MAX(CASE WHEN ts.name = 't1' THEN str.result END) as t1,
    MAX(CASE WHEN ts.name = 't2' THEN str.result END) as t2,
    MAX(CASE WHEN ts.name = 't3' THEN str.result END) as t3,
    MAX(CASE WHEN ts.name = 't4' THEN str.result END) as t4 
FROM 
    sample s 
    JOIN sample_test_result str ON s.id=str.sample_id
    JOIN test_section ts ON str.test_section_id=ts.id
    JOIN section sec ON ts.section_id=sec.id
GROUP BY s.id

Answer 2

您需要条件聚合：

SELECT s.id as sample_id, 
       MAX(CASE WHEN ts.name = 't1' THEN str.result END) as t1,
       . . . 
FROM sample s JOIN 
     sample_test_result str 
     ON s.id=str.sample_id JOIN 
     test_section ts 
     ON str.test_section_id=ts.id
     JOIN section sec ON ts.section_id=sec.id
GROUP BY s.id;

如何将列结果转换为 SQL 中的列 headers？

How do i turn column results into column headers in SQL?

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