MySQL查询耗时138秒，求优化及EXPLAIN结果解读

• product_sub_locations表共701269条数据
• 已为所有关联字段添加索引，但查询仍耗时138秒

查询语句 #

EXPLAIN SELECT
    P.sku,
    PL.name,
    L.name,
    SUM(PSL.qty) as total_qty
FROM
    product_sub_locations PSL
    INNER JOIN products P ON P.id = PSL.product_id
    INNER JOIN categories C ON C.id = P.category_id AND C.is_finish_good = 1
    INNER JOIN sub_locations SL ON SL.id = PSL.sub_location_id
    INNER JOIN locations L ON L.id = SL.location_id
    INNER JOIN locations PL ON PL.id = L.parent_location_id
WHERE
    1 = 1
GROUP BY
    P.id, L.id
ORDER BY
    P.sku, PL.name, L.name

现有查询耗时日志截图及EXPLAIN执行计划截图，恳请帮忙解读EXPLAIN结果，并提供查询性能优化方案。

内容的提问来源于stack exchange，提问作者Hardeep Singh