使用 MAX() 从同一行获取数据？

Question

[MariaDB 10.4，PHP8.0] 我如何重写它才能使其工作，以便它从具有 MAX(total_weight) 的行中 获取 weight_date 并将其列为 highest_weight_date？我读到我们不能在 WHERE 中使用 MAX()？我已经测试过重写几个例子，但是我放弃了并且不好意思展示我最近的尝试：

weight_date HAVING total_weight=MAX(total_weight) AS highest_weight_date

我尝试将其添加到此，但出现错误。 https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=9c057570bd60cdf20a7148189a77fdc4

    SELECT *
           , LEAD(total_weight, 1) OVER(
               ORDER BY weight_date DESC
           ) AS prev_total_weight
           , LEAD(weight_date, 1) OVER(
               ORDER BY weight_date DESC
           ) AS prev_total_weight_date
    
           , MIN(total_weight) OVER() AS lowest_weight
           , MAX(total_weight) OVER() AS highest_weight
 
           , FROM_UNIXTIME(weight_date, '%u') AS weight_week
           , ROW_NUMBER() OVER(
              ORDER BY weight_date DESC
           ) AS RowNum      

    FROM   (
              SELECT *, weight_start_week + weight_end_week AS total_weight
              FROM   YourTable
           ) t
    ORDER BY RowNum

谢谢

Answer 1

要获得 highest_weight_date（具有最高 total_weight 的行中的 weight_date），您只需添加到 select:

FIRST_VALUE(weight_date) OVER (ORDER BY total_weight DESC) AS highest_weight_date

尽管我建议您执行 ORDER BY total_weight DESC, weight_date 或 ORDER BY total_weight DESC, weight_date DESC，这样当权重出现在多个日期时，您可以确定地获得具有该权重的第一个或最后一个日期，而不是任意日期。

fiddle

Answer 2

I have read that we can't use MAX() among with WHERE?

也许这有帮助：使用子查询在 WHERE 子句中查找 MAX() 权重。使用您的示例数据 ...

select from_unixtime( weight_date )
from YourTable
where ( weight_start_week + weight_end_week ) = ( 
  select max( weight_start_week + weight_end_week ) 
  from YourTable 
) ;

-- result
from_unixtime( weight_date )
2022-01-14 00:00:00

DBfiddle

使用 MAX() 从同一行获取数据？

Get data from same row with MAX()?

sql

mariadb

groupwise-maximum

mariadb-10.4