sql-server - SQL中枢轴的变化

Question

我有一个类似的表：

+------+----------+----------+----------+----------+
| Name | Subject1 | Subject2 | Subject3 | Subject4 |
+------+----------+----------+----------+----------+
| x    |       10 |       11 |       12 |       13 |
| y    |       20 |       21 |       22 |       23 |
| z    |       30 |       31 |       32 |       33 |
+------+----------+----------+----------+----------+

我需要得到一个输出：

Name    Subject     Mark
-------------------------------
x   Subject1    10
x   Subject2    11
x   Subject3    12
x   Subject4    13
y   Subject1    20
y   Subject2    21
y   Subject3    22
y   Subject4    23
z   Subject1    30
z   Subject2    31
z   Subject3    32
z   Subject4    33

我需要一个动态查询，因为列的编号和名称在表之间不断变化。每个表至少有 56 列。同样，我有 5 张桌子。

Answer 1

这种将多列转换为多行的过程称为unpivot。如果您有已知值，则可以使用以下内容：

select name, subject, mark
from yourtable 
unpivot
(
  mark
  for subject in (Subject1, Subject2, Subject3, Subject4)
) unpiv;

请参阅SQL Fiddle with Demo。

如果您需要动态执行此操作，那么您将使用动态 SQL：

DECLARE @colsUnpivot AS NVARCHAR(MAX),
   @query  AS NVARCHAR(MAX)

select @colsUnpivot 
  = stuff((select ','+quotename(C.column_name)
           from information_schema.columns as C
           where C.table_name = 'yourtable' and
                 C.column_name <> 'Name'
           for xml path('')), 1, 1, '')

set @query 
  = 'select name, subject, mark
     from yourtable
     unpivot
     (
        mark
        for subject in ('+ @colsunpivot +')
     ) u'

exec sp_executesql @query;

请参阅SQL Fiddle with Demo。

注意：当您对数据列进行反透视时，数据类型必须相同，因此可能需要转换数据。

Answer 2

它应该是这样的（对代码的评论）。（反透视函数文档）

--Initialize variables
DECLARE @Columns VARCHAR(MAX) = ''
DECLARE @UnpivotColumns VARCHAR(MAX) = ''

SELECT @Columns = ',' + @Columns FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'your table'
SELECT @UnpivotColumns = ',' + @UnpivotColumns FROM INFORMATION_SCHEMA.COLUMNS 
WHERE TABLE_NAME = 'your table' AND COLUMN_NAME LIKE 'Subject%'

--Remove first comma
SET @Columns = STUFF(@Columns,1,1,'')
SET @UnpivotColumns = STUFF(@UnpivotColumns,1,1,'')

--Assemble the dynamic query       
DECLARE @qry VARCHAR(Max) = 'SELECT Name, Subject, Mark
FROM 
   (SELECT ' + @Columns + '
   FROM pvt) p
UNPIVOT
   (Mark FOR Subject IN 
      (' + @UnpivotColumns + ')
)AS unpvt;
GO'

--PRINT(@qry)
EXEC (@qry)