Question

我有两个表TESTING和TESTING_BCK，两个都有相同的列。例如。

测试

NR | KEY1 | KEY2 | ... | KEY7 | COMMENTS
 1  |  ...                     | example1
 1  |  ...                     | example2
 ..... and thousands with NR = 1 more
 2  |  ...                     |  null
 2  |  ...                     |  null
 ..... and again many many more

TESTING_BCK

NR | KEY1 | KEY2 | ... | KEY7 | COMMENTS
 2  |  ...                     |  example
 2  |  ...                     |  'this should go to TESTING'
 ..... and again many many more

现在我想更新TESTING，因此TESTING_BCK的评论也将是TESTING的评论（基于密钥）。我知道TESTING_BCK中的所有条目肯定在TESTING中都有相同的键和NR。到目前为止，我这样做了：

UPDATE TESTING
SET COMMENTS = (
        SELECT COMMENTS
        FROM TESTING_BCK
        WHERE TESTING_BCK.NR = TESTING.NR
            AND TESTING_BCK.KEY1 = TESTING.KEY1.....TESTING_BCK.KEY7 = TESTING.KEY7
        )
WHERE EXISTS (
        SELECT COMMENTS
        FROM TESTING_BCK
        WHERE TESTING_BCK.NR = TESTING.NR
            AND TESTING_BCK.KEY1 = TESTING.KEY1
            AND...
        )

但是，当我用数千个条目进行此操作时，这需要永远。有什么想法我怎么能更新TESTING呢？

结果应该是：

测试

    NR | KEY1 | KEY2 | ... | KEY7 | COMMENTS
     1  |  ...                     | example1
     1  |  ...                     | example2
     ..... and thousands with NR = 1 more
     2  |  ...                     |  example
     2  |  ...                     |  'this should go to TESTING'
     2  |  ...                     |  comment from TESTING_BCK
     ......

Answer 1

我认为你应该使用

UPDATE 
(SELECT TESTING.COMMENTS as OLD, TESTING_BCK.COMMENTS as NEW
 FROM TESTING
 INNER JOIN TESTING_BCK
 ON TESTING_BCK.NR = TESTING.NR AND TESTING_BCK.KEY1 = TESTING.KEY1 ..... TESTING_BCK.KEY7 = TESTING.KEY7
) t
SET t.OLD = t.NEW

更新大量行

1 个答案: