尝试获取相关货件的最新状态，但我收到的结果不正确

Question

我目前正在做一个项目，同时试图学习 MySQL，我想加入三个 table 并获取每个相关货件的最新状态。这是我正在使用的 tables（带有示例数据）：

出货量

id	consignee	tracking_number	shipper	weight	import_no
1	JOHN BROWN	TBA99900000121	AMAZON	1	101
2	HELEN SMITH	TBA99900000190	AMAZON	1	102
3	JACK BLACK	TBA99900000123	AMAZON	1	103
4	JOE BROWM	TBA99900000812	AMAZON	1	104
5	JULIA KERR	TBA99900000904	AMAZON	1	105

状态

id	name	slug
1	At Warehouse	at_warehouse
2	Ready For Pickup	ready_for_pickup
3	Delivered	delivered

shipment_status（枢轴table）

id	shipment_id	status_id
1	1	1
2	2	1
3	3	1
4	4	1
5	5	1
6	1	2
7	2	2
8	3	2
9	4	2
10	5	2

所有 table 都有 created_at 和 updated_at 时间戳列

我试图实现的结果示例

slug	shipment_id	status_id
ready_for_pickup	1	2
ready_for_pickup	2	2
ready_for_pickup	3	2
ready_for_pickup	4	2
ready_for_pickup	5	2

这是我根据过去几天所做的示例和研究编写的查询，旨在尝试实现我正在寻找的内容。我发现有时与发货相关的最新状态有时不匹配

SELECT
  statuses.slug AS slug,
  MAX(shipments.id) AS shipment_id,
  statuses.id AS status_id,
FROM
  `shipments`
     INNER JOIN `shipment_status` ON `shipment_status`.`shipment_id` = `shipments`.`id`
     INNER JOIN `statuses` ON `shipment_status`.`status_id` = `statuses`.`id`
     GROUP BY
       `shipment_id`

Answer 1

因为我们需要引用从 MAX 聚合计算的同一记录中的其他字段，你需要分两步完成，还有其他方法，但我发现这个语法更简单：

SELECT
  shipments.id AS id,
  statuses.slug AS slug,
  statuses.id AS status_id,
  shipment_status.shipment_id as shipment_id
FROM
  `shipments`
     INNER JOIN `shipment_status` ON `shipment_status`.`shipment_id` = `shipments`.`id`
     INNER JOIN `statuses` ON `shipment_status`.`status_id` = `statuses`.`id`
WHERE 
   shipment_status.id = (
       SELECT MAX(shipment_status.id)
       FROM `shipment_status`
       WHERE shipment_status.shipment_id = shipments.id
   )

try it out!

此查询假设 id 字段是标识列，因此 MAX(shipment_status.id) 仅代表给定 shipment_id[= 的最新 status 16=]

Answer 2

您可以使用 window 函数：

SELECT s.id, st.slug, st.id
FROM shipments s JOIN
     (SELECT ss.*,
             ROW_NUMBER() OVER (PARTITION BY shipment_id ORDER BY ss.id DESC) as seqnum
      FROM shipment_status ss
     ) ss
     ON ss.shipment_id = s.id JOIN
     statuses st
     ON ss.status_id` = st.id
WHERE ss.seqnum = 1;

另请注意 table 别名的使用，以便查询更易于编写和阅读。

尝试获取相关货件的最新状态，但我收到的结果不正确

Trying to get latest status for related shipment but the results I receive are incorrect

mysql

sql

database

rdbms