使用merge在SQL中合并两个表

2023年8月12日 218次阅读

我有一个问题,我试图合并并合并从一个表到另一个表的数据.

源表和目标表是相同的,除了目标需要在第一列上具有主键.

数据输入和所需结果如下：

data in        Desired results   
 c1 c2 c3       c1   c2    c3  
+--+--+--+    +--+------+------+  
 1  A  x       1  A B C  x y  
 2  B  z       2  B C    z  
 3  A  z       3  A      z x y   
 1  A  y      +--+------+------+  
 3  A  y   
 1  B  x     
 2  C  z     
 1  C  x     
 3  A  x   
 1  A  x   
+--+--+--+

我初始化表格……

CREATE TABLE s (c1 char(2), c2 char(8), C3 char(8))

INSERT INTO s VALUES 
  ('1','A','x'), ('2','B','z'), ('3','A','z'), 
  ('1','A','y'), ('3','A','y'), ('1','B','x'), 
  ('2','C','z'), ('1','C','z'), ('3','A','x'), 
  ('1','A','x')

CREATE TABLE d (c1 char(2) PRIMARY KEY, c2 char(8), C3 char(8))

我可以使用Cursor让它工作……

DECLARE @c1 Char(2)
DECLARE @c2 char(8)
DECLARE @C3 char(8)

DECLARE cur CURSOR FOR SELECT c1, c2, C3 FROM s
OPEN cur
FETCH NEXT FROM cur INTO @c1, @c2, @C3
WHILE @@FETCH_STATUS = 0
BEGIN 
  UPDATE d SET 
    c2 = (CASE WHEN CHARINDEX(RTRIM(@c2), c2) > 0 THEN c2 ELSE SUBSTRING(RTRIM(c2) + ' ' + @c2, 1, 8) END),
    c3 = (CASE WHEN CHARINDEX(RTRIM(@c3), c3) > 0 THEN c3 ELSE SUBSTRING(RTRIM(c3) + ' ' + @c3, 1, 8) END)
    WHERE c1 = @c1
  IF @@ROWCOUNT = 0
  BEGIN
    INSERT INTO d (c1, c2, c3) 
      VALUES (@c1, @c2, @c3)
  END
  FETCH NEXT FROM cur INTO @c1, @c2, @c3
END
CLOSE cur
DEALLOCATE cur

但我无法让Merge工作……
错误：违反PRIMARY KEY约束’PK__d__3213663B03BB8E22′.无法在对象’dbo.d’中插入重复键.重复键值为(1).

MERGE INTO d USING s 
  ON (s.c1 = d.c1)
  WHEN MATCHED THEN 
    UPDATE SET 
      c2 = (CASE WHEN CHARINDEX(RTRIM(s.c2), d.c2) > 0 THEN d.c2 ELSE SUBSTRING(RTRIM(d.c2) + ' ' + s.c2, 1, 8) END),
      c3 = (CASE WHEN CHARINDEX(RTRIM(s.c3), d.c3) > 0 THEN d.c3 ELSE SUBSTRING(RTRIM(d.c3) + ' ' + s.c3, 1, 8) END)
  WHEN NOT MATCHED THEN
    INSERT (c1, c2, c3) VALUES (s.c1, s.c2, s.c3);

有没有办法以比一行一行更优雅的方式做到这一点？

谢谢您的帮助！

最佳答案 您可以使用For XML Path技巧来连接每个组的行,以避免RBAR操作.

;WITH cte1 
     AS (SELECT DISTINCT c1,cs.c2 AS c2 
         FROM   s AS A 
                CROSS apply (SELECT DISTINCT c2 + ' ' 
                             FROM   s AS B 
                             WHERE  A.c1 = B.c1 
                             FOR xml path('')) cs (c2)), 
     cte3 
     AS (SELECT DISTINCT c1,cs.c3 AS c3 
         FROM   s AS A 
                CROSS apply (SELECT DISTINCT c3 + ' ' 
                             FROM   s AS B 
                             WHERE  A.c1 = B.c1 
                             FOR xml path('')) cs (c3)) 
SELECT A.c1, 
       a.c2, 
       b.c3 
FROM   cte1 A 
       INNER JOIN cte3 B 
               ON A.c1 = b.c1

> SQLFIDDLE DEMO

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