SQL中PIVOT和UNPIVOT行列转换

DECLARE @sql_col VARCHAR(8000);
DECLARE @sql_str VARCHAR(8000);
DECLARE @sql_ VARCHAR(MAX);
SELECT  @sql_col = ISNULL(@sql_col + ',', '')
        + QUOTENAME(BBCAccount.dbo.BusinessType.Name)
FROM    BBCAccount.dbo.BusinessType
WHERE   ParentCode IS NULL
        AND Type = 0
        AND IsSystem = 1;
SET @sql_ = 'select *
from(
		select Code,Name  from BBCAccount.dbo.BusinessType WHERE ParentCode IS NULL AND Type=0 AND IsSystem=1
	)as tw
pivot( max(Code) for Name in(' + @sql_col + ') )piv ';
EXEC(@sql_);

明显，UN这个前缀表明了，它做的操作是跟PIVOT相反的，即列转行。UNPIVOT操作涉及到以下三个逻辑处理阶段。

1，生成副本
2，提取元素
3，删除带有NULL的行

UNPIVOT实例

CREATE TABLE pvt
    (
      VendorID INT ,
      Emp1 INT ,
      Emp2 INT ,
      Emp3 INT ,
      Emp4 INT ,
      Emp5 INT
    );
GO
INSERT  INTO pvt
VALUES  ( 1, 4, 3, 5, 4, 4 );
INSERT  INTO pvt
VALUES  ( 2, 4, 1, 5, 5, 5 );
INSERT  INTO pvt
VALUES  ( 3, 4, 3, 5, 4, 4 );
INSERT  INTO pvt
VALUES  ( 4, 4, 2, 5, 5, 4 );
INSERT  INTO pvt
VALUES  ( 5, 5, 1, 5, 5, 5 );
GO
--Unpivot the table.
SELECT  VendorID ,
        Employee ,
        Orders
FROM    ( SELECT    VendorID ,
                    Emp1 ,
                    Emp2 ,
                    Emp3 ,
                    Emp4 ,
                    Emp5
          FROM      pvt
        ) p UNPIVOT
   ( Orders FOR Employee IN ( Emp1, Emp2, Emp3, Emp4, Emp5 ) )AS unpvt;
GO