我的Plex服务器的元数据的日期不正确。我试图将metadata_items.added_at设置为其关联的media_parts.created_at，但您只能通过第三个表（media_items）找到关联。
下面是相关的表模式：

| media_parts                     |
| ------------------------------- |
| id | media_item_id | created_at |

| media_items           |
| --------------------- |
| id | metadata_item_id |

| metadata_items |
| -------------- |
| id | added_at  |

我可以使用3个表的连接来获取信息：

SELECT
    media_parts.created_at AS media_created_at,
    metadata_items.added_at AS metadata_added_at
FROM media_parts
INNER JOIN media_items
ON media_parts.media_item_id = media_items.id
INNER JOIN metadata_items
ON media_items.metadata_item_id = metadata_items.id

但是我很难更新metadata_items表，因为你不能在UPDATE中使用JOIN。

UPDATE metadata_items
SET added_at = (
    SELECT
        media_parts.created_at
    FROM media_parts
    INNER JOIN media_items
    ON media_parts.media_item_id = media_items.id
    INNER JOIN metadata_items
    ON media_items.metadata_item_id = metadata_items.id
)

但它错误百出。
我找到的所有示例都是替换2表连接的解决方案，或者设置一个常量值。

如何使用media_items将metadata_items与media_parts相关联，以便使用created_at中的值更新added_at？

下面是一个sql转储，用于重新生成最小的数据库：

CREATE TABLE media_parts(
   id            INTEGER  NOT NULL PRIMARY KEY 
  ,media_item_id INTEGER  NOT NULL
  ,created_at    VARCHAR(19) NOT NULL
);
INSERT INTO media_parts(id,media_item_id,created_at) VALUES (33,33,'2016-05-13 19:59:06');
INSERT INTO media_parts(id,media_item_id,created_at) VALUES (44,44,'2015-10-12 02:15:21');
INSERT INTO media_parts(id,media_item_id,created_at) VALUES (72,72,'2016-01-01 02:13:58');
INSERT INTO media_parts(id,media_item_id,created_at) VALUES (118,118,'2016-03-05 19:57:32');

CREATE TABLE media_items(
   id               INTEGER  NOT NULL PRIMARY KEY 
  ,metadata_item_id INTEGER  NOT NULL
);
INSERT INTO media_items(id,metadata_item_id) VALUES (33,34);
INSERT INTO media_items(id,metadata_item_id) VALUES (44,45);
INSERT INTO media_items(id,metadata_item_id) VALUES (72,73);
INSERT INTO media_items(id,metadata_item_id) VALUES (118,117);

CREATE TABLE metadata_items(
   id       INTEGER  NOT NULL PRIMARY KEY 
  ,added_at VARCHAR(19) NOT NULL
);
INSERT INTO metadata_items(id,added_at) VALUES (34,'2019-05-13 20:00:54');
INSERT INTO metadata_items(id,added_at) VALUES (45,'2018-10-12 02:19:14');
INSERT INTO metadata_items(id,added_at) VALUES (73,'2019-01-01 02:42:43');
INSERT INTO metadata_items(id,added_at) VALUES (117,'2019-03-07 20:58:50');