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Accepted
Daniel Rikowski
Asked: 2011-08-29 09:40:48 +0800 CST

可以仅使用一个 UPDATE 语句显式保存 ORDER BY 语句的排序吗？

  • 772

我有这张桌子：

SELECT * FROM items

id | item      | position
---|-----------|----------
 1 | USB cable |        0
 2 | SD card   |        4
 3 | Mouse     |        2
 4 | Keyboard  |        0
 5 | Monitor   |        3

对该表进行排序得到以下结果：

SELECT * FROM items ORDER BY position

id | item      | position
---|-----------|----------
 4 | Keyboard  |        0
 1 | USB cable |        0
 3 | Mouse     |        2
 5 | Monitor   |        3
 2 | SD card   |        4

现在我想更新表格并将订单保存在位置列中：

SELECT * FROM items

id | item      | position
---|-----------|----------
 4 | Keyboard  |        1
 1 | USB cable |        2
 3 | Mouse     |        3
 5 | Monitor   |        4
 2 | SD card   |        5

这可以通过单个查询来完成，还是我必须手动遍历所有行并进行手动更新？

如果订单没有完全定义（例如上面的 USB 电缆和键盘），我只是随意决定了订单。

update order-by

2 个回答

  1. Best Answer
    UPDATE
   T1
SET
   position = T2.rn
FROM
   myTable T1
   JOIN
   (
   SELECT
      id,
      ROW_NUMBER() OVER (ORDER BY position) AS rn
   FROM
      myTable
   ) T2 ON T1.id = T2.id

    注意：“键盘”和“USB 数据线”的顺序是任意的。他们都有位置= 0

    要基于项目的抢七位置，请添加辅助排序

          ROW_NUMBER() OVER (ORDER BY position, item) AS rn

    如果您有重复的位置，项目对这也将是任意的......

    • 12

  2. 以下是如何在 MySQL 中实现这一点：

    set @x = 0;
update items A
inner join
(
    select @x:=@x+1 newposition,id
    from items
    order by position
) B using (id)
set A.position=B.newposition;

    我使用了问题中的示例数据，将其加载到笔记本电脑上的 MySQL 5.5.15 中，然后运行了这两行。结果如下：

    mysql> use test
Database changed
mysql> drop table if exists items;
Query OK, 0 rows affected (0.01 sec)

mysql> create table items
    -> (
    ->     id int not null auto_increment,
    ->     item varchar(20),
    ->     position int,
    ->     primary key(id)
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> insert into items (item,position) values
    -> ('USB cable',0),('SD Card',4),
    -> ('Mouse',2),('Keyboard',0),('Monitor',3);
Query OK, 5 rows affected (0.00 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> select * from items;
+----+-----------+----------+
| id | item      | position |
+----+-----------+----------+
|  1 | USB cable |        0 |
|  2 | SD Card   |        4 |
|  3 | Mouse     |        2 |
|  4 | Keyboard  |        0 |
|  5 | Monitor   |        3 |
+----+-----------+----------+
5 rows in set (0.00 sec)

mysql> select * from items order by position;
+----+-----------+----------+
| id | item      | position |
+----+-----------+----------+
|  1 | USB cable |        0 |
|  4 | Keyboard  |        0 |
|  3 | Mouse     |        2 |
|  5 | Monitor   |        3 |
|  2 | SD Card   |        4 |
+----+-----------+----------+
5 rows in set (0.00 sec)

mysql> set @x = 0;
Query OK, 0 rows affected (0.00 sec)

mysql> update items A
    -> inner join
    -> (
    ->     select @x:=@x+1 newposition,id
    ->     from items
    ->     order by position
    -> ) B using (id)
    -> set A.position=B.newposition;
Query OK, 5 rows affected (0.00 sec)
Rows matched: 5  Changed: 5  Warnings: 0

mysql> select * from items;
+----+-----------+----------+
| id | item      | position |
+----+-----------+----------+
|  1 | USB cable |        1 |
|  2 | SD Card   |        5 |
|  3 | Mouse     |        3 |
|  4 | Keyboard  |        2 |
|  5 | Monitor   |        4 |
+----+-----------+----------+
5 rows in set (0.00 sec)

mysql> select * from items order by position;
+----+-----------+----------+
| id | item      | position |
+----+-----------+----------+
|  1 | USB cable |        1 |
|  4 | Keyboard  |        2 |
|  3 | Mouse     |        3 |
|  5 | Monitor   |        4 |
|  2 | SD Card   |        5 |
+----+-----------+----------+
5 rows in set (0.00 sec)
    • 4

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