sql - 是否可以将一个表中的 SELECT 与另一表中的另一个 SELECT 连接到一行中？

Question

我有一个名为“Studies”的表格，它有以下几列:

+-------------+---------------+-------------+------------+-------------+
| CodeStudent |   Type Study  | Title Study | Date Study | Place Study |
+-------------+---------------+-------------+------------+-------------+
|  10         |   Technical   |   TitleOne  | 01-02-2005 |    Narnia   |
+-------------+---------------+-------------+------------+-------------+
|  10         | Technological |   TitleTwo  | 01-05-2009 |    Mars     |
+-------------+---------------+-------------+------------+-------------+
|  10         |   University  |  TitleThree | 01-08-2012 | Gotham City |
+-------------+---------------+-------------+------------+-------------+
|  20         |   Technical   |  OtherTitle | 01-06-2011 |    Namek    |
+-------------+---------------+-------------+------------+-------------+

我有一个名为“学生”的表，其中包含以下列和信息:

+-------------+---------------+-------------+------------+
| CodeStudent |      Name     |   LastName  |  BirthDate |  
+-------------+---------------+-------------+------------+
|  10         |      Hug      |   Lobezno   | 02-02-2002 |
+-------------+---------------+-------------+------------+
|  20         |      Son      |    Gokú     | 05-06-2007 |
+-------------+---------------+-------------+------------+

应考虑以下因素:

• “Students”表的 CodeStudent 列是主键，“Studies”表的 CodeStudent 列是其各自的外键
• 唯一存在的研究类型是技术、科技和大学
• 需要指出的是，并非所有学生都拥有三种类型的学习(技术、技术和大学)，其中一些学生可能有两项学习、一项学习(如孙悟空学生的情况)或没有。

我是否需要知道是否可以在一行中显示所有信息？

如果请求代码为 10 的学生信息，则应显示以下内容:

+-------------+---------------+-------------+------------+-----------------+---------------+----------------+--------------------+-------------------+--------------------+-----------------+----------------+-----------------+
| CodeStudent |      Name     |   LastName  |  BirthDate |  TitleTechnical | DateTechnical | PlaceTechnical | TitleTechnological | DateTechnological | PlaceTechnological | TitleUniversity | DateUniversity | PlaceUniversity |
+-------------+---------------+-------------+------------+-----------------+---------------+----------------+--------------------+-------------------+--------------------+-----------------+----------------+-----------------+
|  10         |      Hug      |   Lobezno   | 02-02-2002 |    TitleOne     |   01-02-2005  |     Narnia     |      TitleTwo      |    01-05-2009     |        Mars        |    TitleThree   |   01-08-2012   |    Gotham City  |
+-------------+---------------+-------------+------------+-----------------+---------------+----------------+--------------------+-------------------+--------------------+-----------------+----------------+-----------------+

如果请求代码为 20 的学生信息，则应显示以下内容:

+-------------+---------------+-------------+------------+-----------------+---------------+----------------+--------------------+-------------------+--------------------+-----------------+----------------+-----------------+
| CodeStudent |      Name     |   LastName  |  BirthDate |  TitleTechnical | DateTechnical | PlaceTechnical | TitleTechnological | DateTechnological | PlaceTechnological | TitleUniversity | DateUniversity | PlaceUniversity |
+-------------+---------------+-------------+------------+-----------------+---------------+----------------+--------------------+-------------------+--------------------+-----------------+----------------+-----------------+
|  20         |      Son      |   Goku      | 05-06-2007 |    OtherTitle   |   01-06-2011  |     Namek      |       NULL         |       NULL        |        NULL        |       NULL      |      NULL      |       NULL      |
+-------------+---------------+-------------+------------+-----------------+---------------+----------------+--------------------+-------------------+--------------------+-----------------+----------------+-----------------+

我知道有一种方法，那就是:

SELECT
      S.CodeStudent, 
      S.Name,
      S.LastName,
      S.BirthDate, 
      (SELECT TOP 1 ST.TitleStudy FROM Studies ST WHERE ST.CodeStudent = 10 AND ST.TypeStudy = 'Technical') AS TitleTechnical,
      (SELECT TOP 1 ST.DateStudy FROM Studies ST WHERE ST.CodeStudent = 10 AND ST.TypeStudy = 'Technical') AS DateTechnical,
      ...
FROM Student S
WHERE S.CodeStudent = 10

但是有没有更好、最优的方法来做到这一点？ :p

Answer 1

使用条件聚合来旋转每种研究类型的列集:

select
    S.CodeStudent
  , S.Name
  , S.LastName
  , S.BirthDate
  , TitleTechnical     = max(case when t.TypeStudy = 'Technical' then t.TitleStudy end)
  , DateTechnical      = max(case when t.TypeStudy = 'Technical' then t.DateStudy end)
  , PlaceTechnical     = max(case when t.TypeStudy = 'Technical' then t.PlaceStudy end)
  , TitleTechnological = max(case when t.TypeStudy = 'Technological' then t.TitleStudy end)
  , DateTechnological  = max(case when t.TypeStudy = 'Technological' then t.DateStudy end)
  , PlaceTechnological = max(case when t.TypeStudy = 'Technological' then t.PlaceStudy end)
  , TitleUniversity    = max(case when t.TypeStudy = 'University' then t.TitleStudy end)
  , DateUniversity     = max(case when t.TypeStudy = 'University' then t.DateStudy end)
  , PlaceUniversity    = max(case when t.TypeStudy = 'University' then t.PlaceStudy end)
from Student S
  left join Studies T  -- left join to support querying students with no studies
    on s.CodeStudent = t.CodeStudent
where S.CodeStudent = 10
group by 
    S.CodeStudent
  , S.Name
  , S.LastName
  , S.BirthDate

rextester 演示:http://rextester.com/SJONU26439