将SQL中的数据转换为新列

我的数据如下：

id maths phy chem 
1   50   60   21
2   60   80   22
3   80   90   23

现在我希望它看起来像：

sub   1   2   3
math 50  60  80 
phy  60  80  90
chem 21  22  23

我的代码：

select *
  from mrks
    pivot
(
  max(maths) 
  for id in ([1], [2], [3])
) piv

然而，我面临两个问题

我无法转换化学值和物理值

不能将数学、物理和化学分为以下几类：

---

在SQL Server中，您可以使用

交叉应用取消pivot，然后使用条件聚合进行透视：

select 
    col,
    max(case when id = 1 then val end) col1,
    max(case when id = 2 then val end) col2,
    max(case when id = 3 then val end) col3
from mytable t
cross apply (values ('maths', maths), ('phy', phy), ('chem', chem)) p(col, val)
group by col

：

col   | col1 | col2 | col3
:---- | ---: | ---: | ---:
chem  |   21 |   22 |   23
maths |   50 |   60 |   80
phy   |   60 |   80 |   90
col | col1 | col2 | col3
:---- | ---: | ---: | ---:
化学| 21 | 22 | 23
数学| 50 | 60 | 80
phy | 60 | 80 | 90
您不能在多个列上执行
PIVOT
，您可以使用
UNION
实现所需的输出，如下所示

SELECT 'Math' AS Sub,*
FROM (SELECT id ,maths FROM mrks) t
PIVOT(MAX(maths) FOR id IN ([1], [2], [3])) piv

UNION ALL

SELECT 'Phy' AS Sub,*
FROM (SELECT id,phy FROM mrks) t
PIVOT(MAX(phy) FOR id IN ([1], [2], [3])) piv

UNION ALL

SELECT 'Chem' AS Sub,*
FROM (SELECT id,chem FROM mrks) t
PIVOT(MAX(chem) FOR id IN ([1], [2], [3])) piv

这也会起作用

DECLARE @tble TABLE (id INT, maths INT, phy INT, chem INT)
INSERT INTO @tble VALUES
(1,50,60,21),(2,60,80,22),(3,80,90,23);

select * from(
SELECT ID,maths AS Scores, 'maths' as Subjects FROM @tble
UNION
SELECT ID,phy AS Scores, 'phy' as Subjects FROM @tble
UNION
SELECT ID,chem AS Scores, 'chem' as Subjects FROM @tble  
  ) s
PIVOT
(
  MIN(Scores) 
  FOR id IN ([1], [2], [3])
) piv

如果有人插入行（4、75、77、81），您预计会发生什么？