1、需求示意圖

2、建立表結構及資料

IF OBJECT_ID('dbo.OpenSchema') IS NOT NULL DROP TABLE dbo.OpenSchema;

CREATE TABLE dbo.OpenSchema
(
  objectid  INT          NOT NULL,
  attribute NVARCHAR(30) NOT NULL,
  value     SQL_VARIANT  NOT NULL, 
  PRIMARY KEY (objectid, attribute)
);
GO

INSERT INTO dbo.OpenSchema(objectid, attribute, value) VALUES
  (1, N'attr1', CAST(CAST('ABC'      AS VARCHAR(10))   AS SQL_VARIANT)),
  (1, N'attr2', CAST(CAST(10         AS INT)           AS SQL_VARIANT)),
  (1, N'attr3', CAST(CAST('20070101' AS SMALLDATETIME) AS SQL_VARIANT)),
  (2, N'attr2', CAST(CAST(12         AS INT)           AS SQL_VARIANT)),
  (2, N'attr3', CAST(CAST('20090101' AS SMALLDATETIME) AS SQL_VARIANT)),
  (2, N'attr4', CAST(CAST('Y'        AS CHAR(1))       AS SQL_VARIANT)),
  (2, N'attr5', CAST(CAST(13.7       AS NUMERIC(9,3))  AS SQL_VARIANT)),
  (3, N'attr1', CAST(CAST('XYZ'      AS VARCHAR(10))   AS SQL_VARIANT)),
  (3, N'attr2', CAST(CAST(20         AS INT)           AS SQL_VARIANT)),
  (3, N'attr3', CAST(CAST('20080101' AS SMALLDATETIME) AS SQL_VARIANT));

-- show the contents of the table
SELECT * FROM dbo.OpenSchema;
GO
 

3、解決方案：

     我們很快會想到用Case When語句來轉換後在Max此項，SQL如下：

SELECT objectid,
  MAX(CASE WHEN attribute = 'attr1' THEN value END) AS attr1,
  MAX(CASE WHEN attribute = 'attr2' THEN value END) AS attr2,
  MAX(CASE WHEN attribute = 'attr3' THEN value END) AS attr3,
  MAX(CASE WHEN attribute = 'attr4' THEN value END) AS attr4,
  MAX(CASE WHEN attribute = 'attr5' THEN value END) AS attr5
FROM dbo.OpenSchema
GROUP BY objectid;
 

很好，這樣也能解決問題。

    我們還可以利用PIVOT來將豎錶轉換為橫表，具體如下：

-- Pivoting Attributes, using PIVOT operator
SELECT objectid, attr1, attr2, attr3, attr4, attr5
FROM dbo.OpenSchema
  PIVOT(MAX(value) FOR attribute
    IN([attr1],[attr2],[attr3],[attr4],[attr5])) AS P;

PIVOT具體語法請baidu。

    當然如下SQL也可以解決問題：

-- PIVOT operator, using table expression
SELECT objectid, attr1, attr2, attr3, attr4, attr5
FROM (SELECT objectid, attribute, value FROM dbo.OpenSchema) AS D
  PIVOT(MAX(value) FOR attribute
    IN([attr1],[attr2],[attr3],[attr4],[attr5])) AS P;
 

結果：

objectid	attr1	attr2	attr3	attr4	attr5
1	ABC	10	2007-01-01 00:00:00.000	NULL	NULL
2	NULL	12	2009-01-01 00:00:00.000	Y	13.700
3	XYZ	20	2008-01-01 00:00:00.000	NULL	NULL