SQL ...如何用同一表中其他行的数据更新行? [英] SQL... How to update rows with data from other rows in the same table?

问题描述

我正在使用MySQL服务器，并且我有一个表，其中某些行缺少数据.我想使用其他行中的信息来更新行.我的桌子看起来像:

I'm using MySQL server and I have a table where some rows are missing data. I would like to update the rows using information from other rows. My table looks something like:

id,signin,deviceId,deviceModel
1,2010-10-12,9ABC9,
2,2010-10-12,3E44F,
3,2010-10-13,D3453,
4,2010-10-14,D3453,
5,2010-10-14,D3453,HW1
6,2010-10-12,3E44F,HW2
7,2010-10-12,9ABC9,HW1

对于前几个条目，deviceModel字段为空.我想使用在同一表的其他行中为deviceId找到的deviceModel更新此值.在上面的示例中，第1行应具有deviceModel = HW1，第2行应具有deviceModel = HW2，依此类推.

For the first few entries, the deviceModel field is empty. I would like to update this value using the deviceModel found for the deviceId in other rows of this same table. In the example above, row 1 should have deviceModel = HW1, row 2 should have deviceModel = HW2, etc.

谢谢！

推荐答案

首先，这是一个非规范化的设计.您应该将deviceModel-> deviceId关系移动到另一个表.

First of all, this is a denormalised design. You should move deviceModel -> deviceId relation to another table.

第二:

UPDATE
  yourTable AS t1
CROSS JOIN (
  SELECT DISTINCT 
    deviceId, deviceModel 
  FROM 
    yourTable 
  WHERE 
    deviceModel IS NOT NULL
) AS t2
USING (deviceId)
SET
  t1.deviceModel = t2.deviceModel
WHERE
  t1.deviceModel IS NULL

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