如何使用 group by 和 Order by DESC 获取表中的最后一行？

Question

我有两个表，表一个名称（ tbl_brands ）与这些列：

和第二个表名（ tbl_loader_attachment ）与这些列：

我使用下面的 MySQL 代码按 DESC 排序：

SELECT tbl_loader_attachment.*, tbl_brands.*  FROM tbl_loader_attachment
INNER JOIN tbl_brands ON(tbl_brands.b_id=tbl_loader_attachment.b_id)
GROUP BY tbl_loader_attachment.b_id ORDER BY tbl_loader_attachment.la_id DESC

当我执行我的代码 select 第一行出现（test1）我想 select 最后一行出现（test4）

Answer 1

一种方法使用GROUP BY查询：

SELECT tla1.*, tb.*
FROM tbl_brands tb
INNER JOIN tbl_loader_attachment tla1
    ON tb.b_id = tla1.b_id
INNER JOIN
(
    SELECT b_id, MAX(la_id) AS max_la_id
    FROM tbl_loader_attachment
    GROUP BY b_id
) tla2
    ON tla1.b_id = tla2.b_id AND
       tla1.la_id = tla2.max_la_id;

如果您使用的是 MySQL 8+（或者该问题的未来读者应该使用 MySQL 8+），那么这里的另一个选项是使用ROW_NUMBER ：

WITH cte AS (
    SELECT *, ROW_NUMBER() OVER (PARTITION BY b_id ORDER BY la_id DESC) rn
    FROM tbl_loader_attachment
)

SELECT tla.*, tb.*
FROM tbl_brands tb
INNER JOIN cte tla ON tb.b_id = tla.b_id
WHERE tla.rn = 1;