基于另一列不为 NULL 将数据从同一列中的一行复制到另一行

Question

我遇到了一个表的问题，该表的某些行缺少数据，我需要从与标题匹配的另一行复制 Artist 列

Plays |  Title                   |  Artist
------+--------------------------+----------------
107   |  Superstition            |  Stevie Wonder
96    |  Superstition            |  NULL
158   |  Patience                |  Guns n Roses
9     |  Patience                |  NULL
112   |  Promised You A Miracle  |  Simple Minds
99    |  Promised You A Miracle  |  NULL
159   |  Baker Street            |  Gerry Rafferty
132   |  Baker Street            |  NULL

我已经阅读了一些关于 SO 的其他问题，这些问题让我有了这个 UPDATE 语句：

UPDATE MetaDataTable
SET Artist = (SELECT TOP 1 Artist FROM MetaDataTable t 
              WHERE (Title = t.Title) AND t.Artist IS NOT NULL)
WHERE Artist IS NULL

最终结果是 TOP 1 Artist 被复制到所有 NULL Artist 列，而不是具有匹配 Title 的 Artist。

Plays |  Title                   |  Artist
------+--------------------------+----------------
107   |  Superstition            |  Stevie Wonder
96    |  Superstition            |  Stevie Wonder
158   |  Patience                |  Guns n Roses
9     |  Patience                |  Stevie Wonder
112   |  Promised You A Miracle  |  Simple Minds
99    |  Promised You A Miracle  |  Stevie Wonder
159   |  Baker Street            |  Gerry Rafferty
132   |  Baker Street            |  Stevie Wonder

我想要的是这样的：

Plays |  Title                   |  Artist
------+--------------------------+----------------
107   |  Superstition            |  Stevie Wonder
96    |  Superstition            |  Stevie Wonder
158   |  Patience                |  Guns n Roses
9     |  Patience                |  Guns n Roses
112   |  Promised You A Miracle  |  Simple Minds
99    |  Promised You A Miracle  |  Simple Minds
159   |  Baker Street            |  Gerry Rafferty
132   |  Baker Street            |  Gerry Rafferty

Artist 为 NULL 的行可以在表中的任何位置，并且不严格低于具有相同标题的完整行。

谢谢！

Answer 1

您需要对 title 列进行表格限定，因为这两个表格是相同的。 Title = t.Title 与 t.Title = t.Title 相同，因为最接近的匹配列是子查询中的表，而不是正在更新的表。将其更改为MetaDataTable.Title = t.title。

UPDATE MetaDataTable
   SET Artist = (SELECT TOP 1 Artist FROM MetaDataTable t WHERE MetaDataTable.Title = t.Title AND t.Artist IS NOT NULL)
WHERE Artist IS NULL

Answer 2

我建议使用可更新的 CTE：

WITH toupdate as (
      SELECT mdt.*,
             MAX(mdt.artist) OVER (PARTITION BY mdt.title) as imputed_artist
      FROM MetaDataTable mdt
     )
UPDATE toupdate
   SET Artist = imputed_artist
WHERE Artist IS NULL;