Question

假设我有一个这样的数据库设置，我想通过将优先级更改为最后一个数字+ 1来将Milk移到最后。

id | item | priority
---|------|----------   
[...]
26 | Milk | 1
27 | Eggs | 2
28 | Ham  | 3

所以我需要运行这样的东西

UPDATE shopping SET priority = (SELECT priority FROM shopping ORDER BY priority DESC LIMIT 1) + 1 WHERE id = '26'

并最终得到类似的东西

id | item | priority
---|------|----------   
[...]
27 | Eggs | 2
28 | Ham  | 3
26 | Milk | 4

如何正确地执行？

Answer 1

UPDATE `shopping` s, (
    SELECT
        MAX(`priority`) AS 'maxPriority',
        MAX(`id`) AS 'maxId'
    FROM `shopping`
) t
SET
    s.`priority` = t.`maxPriority` + 1,
    s.`id` = t.`maxId` + 1
WHERE s.`id`=26
AND s.`priority` != t.`maxPriority`
# this ensures that it's not the one that's
# already holding the max priority

Answer 2

您的请求可能是：

UPDATE shopping SET priority = (select max(priority)+1) where id=26;

但这不起作用，您必须对请求，来源和详细信息进行相同的更改：

http://the-stickman.com/uncategorized/mysql-update-with-select-on-the-same-table-in-the-same-query/

使用其他查询结果更新行

2 个答案: