sql - 使用合并在 SQL 中合并两个表

Question

我在尝试将数据从一个表合并到另一个表时遇到问题。

源表和目标表是相同的，只是目标表的第一列需要有一个主键。

数据输入和期望结果如下:

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...

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。重复的键值为 (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);

有没有比一行一行更优雅地做到这一点的方法？

谢谢您的帮助!

Answer 1

您可以避免 RBAR 操作使用 For XML Path连接每组行的技巧。

;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 

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