INSERT ... ON DUPLICATE KEY UPDATE row IF date_added > VALUES(date_added)

Question

如果满足特定条件，我如何 INSERT 和 ON DUPLICATE KEY 更新整行？我想更新整个 row 如果 VALUES(date_added) 比 table 旧 date_added。

我看过这篇文章：

https://thewebfellas.com/blog/conditional-duplicate-key-updates-with-mysql

INSERT INTO daily_events
  (created_on, last_event_id, last_event_created_at)
VALUES
  ('2010-01-19', 23, '2010-01-19 10:23:11')
ON DUPLICATE KEY UPDATE
  last_event_id = IF(last_event_created_at < VALUES(last_event_created_at), VALUES(last_event_id), last_event_id),
  last_event_created_at = IF(last_event_created_at < VALUES(last_event_created_at), VALUES(last_event_created_at), last_event_created_at);

但这不是编写语句的灵活方式。

稍后编辑：

首先，因为条件是针对每个将要更新的字段进行评估的，其次，因为您必须注意将更新条件列的行定位在语句的最后位置。否则你会用错误毒化 UPDATE。

更确切地说，我希望我反转了两个 UPDATE 行的语句也有效：

INSERT INTO daily_events(created_on, last_event_id, last_event_created_at) VALUES('2010-01-19', 23, '2010-01-19 10:23:11') ON DUPLICATE KEY UPDATE last_event_created_at = GREATEST(last_event_created_at, VALUES(last_event_created_at)), last_event_id = (CASE WHEN last_event_created_at < VALUES(last_event_created_at) THEN VALUES(last_event_id) ELSE last_event_id END);

这是不可能的，因为：

An important thing to keep in mind when using this approach is that the order in which you update your fields is very important. I was wrongly under the impression that the updates took place in one mass-assignment after the entire query had been interpreted by MySQL. But they’re not: the assignments happen in the order they appear in the query.

When the update is executed with a more recent event, the last_event_created_at field will be updated, but the last_event_id field won’t. This is because when the second IF is evaluated last_event_created_at has already been updated so that last_event_created_at is equal to VALUES(last_event_created_at). Crazy huh?!

Answer 1

您的查询似乎符合您的要求，所以我没有完全理解您的问题。您可以使用 GREATEST():

来简化它

INSERT INTO daily_events(created_on, last_event_id, last_event_created_at)
    VALUES('2010-01-19', 23, '2010-01-19 10:23:11')
ON DUPLICATE KEY UPDATE
  last_event_id = (CASE WHEN last_event_created_at < VALUES(last_event_created_at) THEN VALUES(last_event_id) ELSE last_event_id END),
  last_event_created_at = GREATEST(last_event_created_at, VALUES(last_event_created_at));

（使用 CASE 是对等效功能的 ANSI 标准的偏好。）

MySQL 没有提供表达 "update all of these when this condition is met".

的方式

INSERT ... ON DUPLICATE KEY UPDATE row IF date_added > VALUES(date_added)

INSERT ... ON DUPLICATE KEY UPDATE row IF date_added > VALUES(date_added)

mysql

insert

duplicates

insert-update