如何使用其他记录作为值来更新 sql 中的记录？

Question

MS SQL Server 2008 - 我有一个 db 表，其中我有一小部分行接近匹配，除了 2 列，在表的其他地方。你将如何构建一个 SQL 更新循环来遍历子集 (record1) 并搜索其匹配的对应项 (record2)，然后从列 (record2.columnX) 复制一个值以更新另一个 (record1.columnX)？

之前：

TxID|RecordID|ColumnA|ColumnX|ColumnY    
1   |111.222 |ggg    |1234   |subset1
2   |111.222 |ggg    |3456   |subset2
3   |111.333 |hhh    |6789   |subset1
4   |111.333 |hhh    |7890   |subset2
5   |111.444 |jjj    |2345   |subset1
5   |111.444 |jjj    |5678   |subset2

之后：

TxID|RecordID|ColumnA|ColumnX|ColumnY    
1   |111.222 |ggg    |1234   |subset1
2   |111.222 |ggg    |1234   |subset2
3   |111.333 |hhh    |6789   |subset1
4   |111.333 |hhh    |6789   |subset2
5   |111.444 |jjj    |2345   |subset1
5   |111.444 |jjj    |2345   |subset2

自学成才，对 SQL 比较陌生。耐心是值得的。

Answer 1

您可以通过 RecordID 对 min(TxID) 组使用内部联接的更新

  update my_table t1
  inner join 
  (
      select RecordID, ColumnA, ColumnX, ColumnY
      from my_table 
      where (TxID, RecordID ) in (
        select min(TxID), RecordID 
      from my_table 
      group by RecordID) 
  ) ttt on ttt.RecordID = t1.RecordID  
  set  t1.ColumnX = ttt.ColumnX

Answer 2

我会这样做：

UPDATE table t1 SET columnX=sq.columnXmin
FROM  (
   SELECT t2.RecordID, MIN(t2.columnX) as columnXmin
   FROM   table t2
   GROUP  BY t2.RecordID
   ) AS sq
WHERE  t1.RecordID = sq.RecordID;

Answer 3

另一种方法：

UPDATE  t1
SET     t1.ColumnX = t2.ColumnX
FROM    @table t1
        INNER JOIN @table t2 ON t1.RecordID = t2.RecordID
                                AND t1.ColumnA = t2.ColumnA
                                AND t1.ColumnY <> t2.ColumnY
                                AND t1.TxID > t2.TxID -- the lowest TxID keeps its original value

或者……

UPDATE  t1
SET     t1.ColumnX = t2.ColumnX
FROM    @table t1
        INNER JOIN @table t2 ON t1.RecordID = t2.RecordID
                                AND t1.ColumnA = t2.ColumnA
                                AND t1.ColumnY <> t2.ColumnY
                                AND t1.TxID < t2.TxID -- the largest TxId keeps its original value