MERGE使用源行来定位列？

Question

我有一些结构良好的数据,如下所示:

CREATE TABLE SourceBodyPartColors
(
 person_ID INTEGER NOT NULL, 
 body_part_name VARCHAR(5) NOT NULL
    CHECK (body_part_name IN ('hair', 'eye', 'teeth')), 
 color VARCHAR(20) NOT NULL, 
 UNIQUE (color, body_part_name, person_ID)
);

INSERT INTO SourceBodyPartColors (person_ID, body_part_name, color)
   VALUES (1, 'eye', 'blue'), 
          (1, 'hair', 'blond'), 
          (1, 'teeth', 'white'), 
          (2, 'hair', 'white'), 
          (2, 'teeth', 'yellow'), 
          (3, 'hair', 'red');

可悲的是,目标结构不是很好,看起来更像是这样:

CREATE TABLE TargetBodyPartColors
(
 person_ID INTEGER NOT NULL UNIQUE, 
 eye_color VARCHAR(20), 
 hair_color VARCHAR(20), 
 teeth_color VARCHAR(20)
);

INSERT INTO TargetBodyPartColors (person_ID)
   VALUES (1), (2), (3);

我可以UPDATE像这样写一个SQL-92 :

UPDATE TargetBodyPartColors
   SET eye_color = (
                    SELECT S1.color
                      FROM SourceBodyPartColors AS S1
                     WHERE S1.person_ID 
                              = TargetBodyPartColors.person_ID
                           AND S1.body_part_name = 'eye'
                   ), 
       hair_color = (
                     SELECT S1.color
                       FROM SourceBodyPartColors AS S1
                      WHERE S1.person_ID 
                               = TargetBodyPartColors.person_ID
                            AND S1.body_part_name = 'hair'
                    ), 
       teeth_color = (
                      SELECT S1.color
                        FROM SourceBodyPartColors AS S1
                       WHERE S1.person_ID 
                                = TargetBodyPartColors.person_ID
                             AND S1.body_part_name = 'teeth'
                     );

......但重复的代码困扰着我.

MERGE我想,这是一个简化使用的好地方,但我无法想出任何合理的东西.

有关如何使用MERGE此数据的任何想法.(注意:我想避免专有UPDATE..FROM syntax,谢谢.)

Answer 1

WITH Pivoted AS
(
  SELECT person_ID, eye, hair, teeth
  FROM SourceBodyPartColors
    PIVOT
    (
    MAX (color) FOR body_part_name IN ( [eye], [hair], [teeth] )
    ) AS pvt
  )  
MERGE TargetBodyPartColors AS target
USING  Pivoted AS source
ON (target.person_ID = source.person_ID)
WHEN MATCHED THEN 
UPDATE SET eye_color = source.eye,  
           hair_color = source.hair,  
           teeth_color = source.teeth ;