mySQL - 使用select返回多行来更新多个列

I have a table of postcodes and I want to update each postcode with its 3 nearest neighbours. Ie to fill in the blanks in this table:

我有一个邮政编码表，我想用3个最近的邻居更新每个邮政编码。即填写此表中的空白：

postcode  nearestPostcode1  nearestPostcode2  nearestPostcode3
_______________________________________________________________

KY6 1DA      -                -                  -
KY6 1DG      -                -                  -
KY6 2DT      -                -                  -
KY6 1RG      -                -                  -
....

I've figured out a SELECT query to find the nearest postcodes and here is one clumsy way the first row could be updated:

我已经找到了一个SELECT查询来查找最近的邮政编码，这是第一行可以更新的一种笨拙的方式：

update table1 set 
nearestPostcode1 = (select query for returning the first nearest postcode),
nearestPostcode2 = (select query for returning the second nearest postcode),
nearestPostcode3 = (select query for returning the third nearest postcode)
where postcode = 'KY6 1DA';

However this will result in 3 select queries being run for each row update. It would be more efficient if there was some way to do what is expressed by this pseudo code:

但是，这将导致为每个行更新运行3个选择查询。如果有一些方法来执行这个伪代码所表达的内容，那将会更有效：

update table1 set 
(nearestPostcode1, nearestPostcode2, nearestPostcode3) = 
(select query to return the 3 nearest postcodes)
where postcode = 'KY6 1DA';

The 'select query' in the above looks like this:

上面的“选择查询”如下所示：

select postcode from postcodeTable 
order by <equation to calculate distance> ASC 
limit 3

Is there anyway for the rows returned from the select to be put into a form that they can be used to update multiple fields? Thanks.

无论如何，从select返回的行被放入一个可以用来更新多个字段的表单中吗？谢谢。

4 个解决方案

#1

Update Table1
    Cross Join  (
                Select Min( Case When Z1.Num = 1 Then Z1.postcode End ) As PostCode1
                    , Min( Case When Z1.Num = 2 Then Z1.postcode End ) As PostCode2
                    , Min( Case When Z1.Num = 3 Then Z1.postcode End ) As PostCode3
                From    (
                        Select postcode 
                            , @num := @num + 1 As Num
                        From postcodeTable 
                        Where postcode = 'KY6 IDA'
                        Order By <equation to calculate distance> ASC 
                        Limit 3
                        ) As Z1
                ) As Z
Set nearestPostCode1 = Z.PostCode1
    , nearestPostCode2 = Z.PostCode2
    , nearestPostCode3 = Z.PostCode3
Where Table1.postcode =  'KY6 IDA'

#2

You can do something similar to this:

你可以做类似的事情：

UPDATE table1
SET
nearestPostcode1 = pc1,
nearestPostcode2 = pc2,
nearestPostcode3 = pc3
FROM 
(SELECT pc1, pc2, pc3 FROM ....) t
WHERE 
postcode = 'KY6 1DA';

I found this related question on * on how to transform columns to rows:

我在*上找到了关于如何将列转换为行的相关问题：

MySQL - Rows to Columns

MySQL - 行到列

In your case, you can do something like

在你的情况下，你可以做类似的事情

SELECT 
IF(@rownum=1,postcode,'') ) AS pc1, 
IF(@rownum=2,postcode,'') ) AS pc2, 
IF(@rownum=3,postcode,'') ) AS pc2, 
FROM
(SELECT postcode 
FROM postcodeTable 
ORDER BY <equation to calculate distance> ASC 
LIMIT 3)

Here is a hack to simulate the ROW_NUMBER() functionality in MySQL [1]:

这是一个模拟MySQL [1]中的ROW_NUMBER（）功能的hack：

SELECT @rownum:=@rownum+1 rownum, t.*
FROM (SELECT @rownum:=0) r, mytable t;

#3

I think you could do this with the pseudo-code:

我想你可以用伪代码做到这一点：

REPLACE INTO table1 (postcode, nearestPostcode1, nearestPostcode2, nearestPostcode3)
    SELECT "KY6 1DA", col1, col2, col3 FROM myTable WHERE ...;

it'd be easier to specify it seeing the real SQL.

看到它真正的SQL就更容易了。

Note the first column is specified as a constant in quotes. For this to work postcode must be a UNIQUE or PRIMARY index.

请注意，第一列被指定为引号中的常量。为此，邮政编码必须是UNIQUE或PRIMARY索引。

#4

-1

Anytime I see a table with columns that have 1-up counters after their names, I get concerned.

任何时候我看到一个表格，其列名在他们的名字后面有一个计数器，我很担心。

In general, it is a Bad Idea (TM) to store data that can be calculated from data that is already stored. What happens if your application all of a sudden needs the 4 closest postal codes? What if the postal code boundaries change?

通常，存储可以从已经存储的数据计算的数据是坏想法（TM）。如果您的应用程序突然需要4个最接近的邮政编码，会发生什么？如果邮政编码边界发生变化怎么办？

Assuming the distance calculation isn't very complex, you'll be better off in the long run not explicitly storing this data.

假设距离计算不是很复杂，从长远来看，你最好不要明确地存储这些数据。

#1

Update Table1
    Cross Join  (
                Select Min( Case When Z1.Num = 1 Then Z1.postcode End ) As PostCode1
                    , Min( Case When Z1.Num = 2 Then Z1.postcode End ) As PostCode2
                    , Min( Case When Z1.Num = 3 Then Z1.postcode End ) As PostCode3
                From    (
                        Select postcode 
                            , @num := @num + 1 As Num
                        From postcodeTable 
                        Where postcode = 'KY6 IDA'
                        Order By <equation to calculate distance> ASC 
                        Limit 3
                        ) As Z1
                ) As Z
Set nearestPostCode1 = Z.PostCode1
    , nearestPostCode2 = Z.PostCode2
    , nearestPostCode3 = Z.PostCode3
Where Table1.postcode =  'KY6 IDA'

#2