mysql - 按日期时间区分最后两条记录的值

Question

我有一个表，我需要在每个 *item_id* 的最后两次运行id, item_id, value (int), run (datetime)之间选择值差异。

Answer 1

SELECT item_id, ABS(value1 - value2) AS diff
FROM (  SELECT h.item_id, h.value AS value1, h2.value AS value2
        FROM (  SELECT id, item_id, value
                FROM table_name
                GROUP BY item_id
                ORDER BY run DESC) AS h
        INNER JOIN (    SELECT id, item_id, value
                        FROM table_name
                        ORDER BY run DESC) AS h2
        ON h.item_id = h2.item_id AND h.id != h2.id
        GROUP BY item_id) AS h3

我相信这应该对你有用。只需替换table_name为正确的名称。

说明：
基本上我将表与自身按run DESC顺序加入，根据 item_id 和 id 加入它们。然后我再次对它们进行 GROUP BY 以删除潜在的第 3 次等情况。最后我通过 ABS(value1 - value2) 计算它们之间的差异。

Answer 2

    SELECT t2.id, t2.item_id, (t2.value- t1.value) valueDiff, t2.run
    FROM ( table_name AS t1 
           INNER JOIN 
           table_name AS t2 
           ON t1.run = (SELECT MAX(run) FROM table_name where run < t2.run) 
                 and t1.item_id = t2.item_id) 

这是假设您想要记录与上次运行的记录之间的差异