MySQL：子查询优化问题，其中子查询检查超过14000行

我需要帮助来优化下面的子查询。简言之，我有以下查询，其中树表根据子查询条件在s_id和分支表的最大时间戳上连接分支表

我对这个查询返回的结果很满意。但是，这个查询非常慢。瓶颈是检查14000多行的从属子QueryBranch2。如何优化子查询以加速此查询

SELECT *                
FROM dept.tree tree              
    LEFT JOIN dept.branch branch ON tree.s_id = branch.s_id                    
        AND branch.timestamp =
            (
                SELECT MAX(timestamp)                                   
                FROM dept.branch branch2 
                WHERE branch2.s_id = tree.s_id 
                AND branch2.timestamp <= tree.timestamp
            )                
WHERE tree.timestamp BETWEEN CONVERT_TZ('2020-05-16 00:00:00', 'America/Toronto', 'UTC') 
AND CONVERT_TZ('2020-05-16 23:59:59', 'America/Toronto', 'UTC') 
AND tree.s_id IN ('459','460')                
ORDER BY tree.timestamp ASC;

表分支：

   id     box_id        timestamp                  data
373001345   1       2020-05-07 06:00:20     {"R": 0.114, "H": 20.808}
373001395   1       2020-05-07 06:02:26     {"R": 0.12, "H": 15.544}
373001462   1       2020-05-07 06:03:01     {"R": 0.006, "H": 55.469}
373001494   1       2020-05-07 06:04:38     {"R": 0.004, "H": 51.85}
373001496   1       2020-05-07 06:05:18     {"R": 0.02, "H": 5.8965}
373001497   1       2020-05-07 06:06:39     {"R": 0.12, "H": 54.32}
373001510   2       2020-05-07 06:07:09     {"R": 0.34, "H": 1.32}
373001511   2       2020-05-07 06:07:29     {"R": 0.56, "H": 32.7}

分支具有s_id和时间戳索引

我使用的是5.7.25-google-log版本

解释如下：

    id    select_type        table     partitions    type    possible_keys    key    key_len    ref    rows    filtered     Extra
    1   PRIMARY tree        range   unique_timestamp_s_id,idx_s_id_timestamp,idx_timestamp  idx_s_id_timestamp  10      2629    100.00  Using index condition; Using filesort
    1   PRIMARY branch      ref unique_timestamp_s_id,idx_timestamp unique_timestamp_s_id   5   func    1   100.00  Using where
    2   DEPENDENT SUBQUERY  branch2     ref unique_timestamp_s_id,idx_s_id_timestamp,idx_timestamp  idx_s_id_timestamp  5   tree.s_id   14122   33.33   Using where; Using index

请提供“显示创建表”

分支需要INDEXs_id和时间戳

你需要留下吗？这可能会无缘无故地减慢查询速度

一个色谱柱上的IN和另一个色谱柱上的IN之间的组合可能未得到很好的优化；你正在运行哪个版本

请提供解释选择，以便我们讨论它是否得到了很好的优化。如果不是，我们可以讨论如何将变体中的转换为联合

这实际上可能比我上面所想的方法要快

使用上面的索引，然后重写查询：

SELECT b.*
    FROM ( SELECT  s_id,
                   MAX(timestamp) as timestamp                                
               FROM dept.branch 
               WHERE timestamp BETWEEN
                      CONVERT_TZ('2020-05-16 00:00:00', 'America/Toronto', 'UTC')
                  AND CONVERT_TZ('2020-05-16 23:59:59', 'America/Toronto', 'UTC')
                 AND s_id IN ('459','460')                
         ) AS x
    JOIN dept.branch AS b  USING(s_id, timestamp)

首先，看看这是否得到了正确的信息。然后，如果您需要帮助，我将在子查询中解释如何进行联合。

这将更快：

select
    tree.s_id, tree.timestamp, branch.data
from
    (
        SELECT
            tree.s_id, tree.timestamp, max(branch.timestamp) as max_branch_timestamp
        FROM
            dept.tree tree
                LEFT JOIN dept.branch branch
                ON(
                        branch.s_id      =  tree.s_id
                    and branch.timestamp <= tree.timestamp
                )
        WHERE
            tree.timestamp BETWEEN
                CONVERT_TZ('2020-05-16 00:00:00', 'America/Toronto', 'UTC') AND
                CONVERT_TZ('2020-05-16 23:59:59', 'America/Toronto', 'UTC')
        AND tree.s_id IN ('459','460')                
        group by tree.s_id, tree.timestamp
    ) tree
        left outer join branch
        on(
                branch.s_id      = tree.s_id
            and branch.timestamp = tree.max_branch_timestamp
        )

---

示例数据、期望的结果以及对您想要实现的逻辑的解释都会有所帮助。或者，请稍等几分钟。MySQL的确切版本是什么？这是groupwise max？我在上面添加了更多信息。我很抱歉没有提前添加它们。如果我需要提供更多细节，请告诉我。谢谢，我提供了更多的信息，如果有帮助，请告诉我。我很抱歉没有早点提供。我对重新分级您的查询有疑问，您是否加入dept.tree而不是dept.branch？上面的查询给出以下错误：错误代码：1140。在没有分组依据的聚合查询中，选择列表的表达式1包含未聚合的列“dept.s_id”；这与sql\u mode=only\u full\u group\u byOops不兼容。我需要再看一次

select
    tree.s_id, tree.timestamp, branch.data
from
    (
        SELECT
            tree.s_id, tree.timestamp, max(branch.timestamp) as max_branch_timestamp
        FROM
            dept.tree tree
                LEFT JOIN dept.branch branch
                ON(
                        branch.s_id      =  tree.s_id
                    and branch.timestamp <= tree.timestamp
                )
        WHERE
            tree.timestamp BETWEEN
                CONVERT_TZ('2020-05-16 00:00:00', 'America/Toronto', 'UTC') AND
                CONVERT_TZ('2020-05-16 23:59:59', 'America/Toronto', 'UTC')
        AND tree.s_id IN ('459','460')                
        group by tree.s_id, tree.timestamp
    ) tree
        left outer join branch
        on(
                branch.s_id      = tree.s_id
            and branch.timestamp = tree.max_branch_timestamp
        )