如何将列 UNPIVOT 转换为行？

Question

考虑下表#document_fields

id   x   y    z
------------------
1  foo  bar  baz
2  one  two  three
3  aaa  bbb  ccc
4  123  456  789

列数可能会有所不同，列名也会有所不同。我需要将列转成这样的行：

id  field value
---------------
1   x     foo
1   y     bar
1   z     baz
2   x     one
2   y     two
2   z     three
.
.
3   z     789

我正在尝试了解 SQL Server 中枢轴的工作方式，但没有比这更进一步的了：

select 
      *
into
      #document_fields_pivot
from (
      select * from (
            select *
            from #document_fields
      ) t
      pivot (
            -- ??
      ) p
  ) tbl

谁能帮我完成这个查询/解释我旋转？非常感谢任何帮助。

Answer 1

你想要的是 UNPIVOT 并这样做：

select id,field,value from
#document_fields
unpivot
(
 value
 for field in (x,y,z)
) as u
order by id,field

Demo

Answer 2

DECLARE @Component table (ComponentId INT,Descr VARCHAR(10),Descr1 VARCHAR(10),Descr2 VARCHAR(10))
INSERT INTO @Component (ComponentId,Descr,Descr1,Descr2)values (1,'foo','bar','baz')
INSERT INTO @Component (ComponentId,Descr,Descr1,Descr2)values (2,'one','two','three')
INSERT INTO @Component (ComponentId,Descr,Descr1,Descr2)values (3,'aaa','bbb','ccc')
INSERT INTO @Component (ComponentId,Descr,Descr1,Descr2)values (3,'123','456','789')


   select
      ComponentId,Field
   from @Component P

 UNPIVOT
 (
   Field
   FOR Value
   IN (
    [Descr],[Descr1],[Descr2]
   )
 ) PivotTable;