带有 MAX() 的 GROUP BY 返回错误的行 ID

Question

我想在执行请求时获得每个 order_product_id 每周的最大使用容量。 WHERE 子句中的 JOIN 或 SELECT 变体不起作用，因为 max_capacity 对某些 order_product_id 重复。我的查询每周返回正确的 order_product_id 和 max_capacity，但没有返回正确的行 ID。

CREATE TABLE `capacity_log` (
`id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
`date_occurred` DATETIME NOT NULL,
`ip_address` VARCHAR(255) NOT NULL DEFAULT '',
`order_product_id` INT UNSIGNED NOT NULL,
`serial` VARCHAR(255) NOT NULL DEFAULT '',
`used_capacity` BIGINT NULL DEFAULT NULL,
`aux2` INT NULL DEFAULT NULL,
`request` BLOB NULL,
`retry_count` INT NOT NULL DEFAULT '0',
`fetch_time` INT NOT NULL DEFAULT '0',
`response` BLOB NULL,
`custom_fetch_time` INT NOT NULL DEFAULT '0',
PRIMARY KEY (`id`),
INDEX `user_id` (`order_product_id`))

我的查询：

SELECT  c.order_product_id, MAX(c.used_capacity) AS `max_capacity`
FROM capacity_log c
WHERE c.date_occurred < '2020-10-1' AND c.aux2 IS NULL 
GROUP BY
    YEAR(c.date_occurred), WEEK(c.date_occurred),
    c.order_product_id
    

Answer 1

您想要整行，因此聚合不是您所追求的。相反，您需要过滤。一种选择使用子查询：

select c.*
from capacity_log c
where c.id = (
    select c1.id
    from capacity_log c1
    where  
        c1.date_occurred < '2020-10-1' 
        and c1.aux2 is null
        and c1.order_product_id = c.order_product_id
        and yearweek(c1.date_occurred) = yearweek(c.date_occurred)
    order by c1.used_capacity desc limit 1
)

我们可以像这样优化子查询的where子句：

    where  
        c1.date_occurred < '2020-10-1' 
        and c1.aux2 is null
        and c1.order_product_id = c.order_product_id
        and c1.date_occurred >= c.date_occurred - interval weekday(c.date_occurred) day
        and c1.date_occurred <  c.date_occurred - interval weekday(c.date_occurred) day + interval 7 day

为了提高性能，您需要在(order_product_id, aux2, date_occurred, used_capacity, id) 上建立索引。