如何使用group by和Order by DESC获取表中的最后一行？

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+（或者将来的读者应该使用MySQL 8+），那么这里的另一种选择是使用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;