MYSql window 函数 - 获取最后一个值

Question

我正在尝试获取特定时间玩家余额的最新值window。

我有一个 transactions table.

玩家余额不是最大值或最小值

SELECT  project_id, 
        player_id,
        FIRST_VALUE(balance) OVER (PARTITION BY player_id ORDER BY event_arrival_time DESC) AS balance
FROM transactions
WHERE event_arrival_time BETWEEN '2019-12-02 00:00:00' AND '2019-12-03 23:59:59'
        AND project_id='aaa' 
GROUP BY project_id, player_id

我得到了值，但是如果我使用针对单个玩家的查询来测试它们，我会得到不同的平衡，并且我会在期间中间的某个地方看到给定的结果平衡。

此外，如果我多次运行这个查询，我会得到不同的余额，就像它选择不同的交易（我们说的是 10 分钟的差异）。

SELECT * 
FROM transacitions
where event_arrival_time BETWEEN '2019-12-02 00:00:00' AND '2019-12-03 23:59:59'
        AND project_id='aaa' and player_id = 'player1'
ORDER BY event_arrival_time desc

我想获得那个时期的玩家列表，以及他们的最新余额（不是最大值 - 也许是最大日期）。

Answer 1

您需要过滤，而不是聚合。

您可以使用相关子查询来做到这一点：

SELECT project_id, player_id, balance
FROM transactions t
WHERE event_arrival_time = (
    SELECT MAX(t1. event_arrival_time)
    FROM transactions t1
    WHERE 
        t1.player_id = t.player_id
        AND t1.event_arrival_time >= '2019-12-02'
        AND t1.event_arrival_time < '2019-12-03'
        AND t1.project_id = 'aaa' 
    )

为了性能，您需要 (project_id, player_id, event_arrival_time) 上的索引。您也可以尝试 covering 索引：(project_id, player_id, event_arrival_time, balance)；使用这样的索引，数据库可能仅通过查看索引来执行整个查询，而不实际访问基础数据。

您还可以使用 window 函数：


SELECT project_id, player_id, balance
FROM (
    SELECT 
        t.*,
        RANK() OVER(PARTITION BY player_id ORDER BY event_arrival_time DESC) rn
    FROM transactions t
    WHERE
        event_arrival_time >= '2019-12-02'
        AND event_arrival_time < '2019-12-03'
        AND project_id='aaa'
) t
WHERE rn = 1

Answer 2

删除 GROUP BY 子句，如果需要，在 SELECT:

中使用 DISTINCT

SELECT DISTINCT 
  project_id, 
  player_id,
  FIRST_VALUE(balance) OVER (PARTITION BY player_id ORDER BY event_arrival_time DESC) AS balance
FROM transactions
WHERE event_arrival_time BETWEEN '2019-12-02 00:00:00' AND '2019-12-03 23:59:59'
  AND project_id='aaa'

Answer 3

我认为这应该可行。没有样品很难说。

SELECT
     t.project_id,
     t.player_id,
     GROUP_CONCAT(t.balance) AS Balance -- supposed to have single value
FROM transacitions t
LEFT JOIN transactions t2 ON t.project_id = t2.project_id AND t.player_id = t2.player_id
AND t.event_arrival_time < t2.event_arrival_time
where t2.player_id IS NULL
AND t.event_arrival_time BETWEEN '2019-12-02 00:00:00' AND '2019-12-03 23:59:59'
GROUP BY t.project_id, t.player_id
ORDER BY t.event_arrival_time desc

MYSql window 函数 - 获取最后一个值

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