编辑1：

Question

我有一个非常简单的Maria DB用于家庭自动化。这是我的ER的基本摘录：

<div id="my-container"> <div class="container h-40"> <div class="row align-items-center mt-3"> <div class="col-6 text-center"> <img width="150" height="150" src="img/user-placeholder.svg"> <p class="mt-2 mb-0">pholder</p> </div> <div class="col-6"> <div class="mb-2"> <div class="row"> <div class="col-6 text-center">pholder</div> <div class="col-6 text-center">pholder</div> </div> <div class="row"> <div class="col-6 text-center">Friends</div> <div class="col-6 text-center">Posts</div> </div> </div> <butto class="btn btn-transparent mt-2">Click</button> </div> </div> <br> <p class="text-center m-0">Contents</p> <hr class="mt-0 mb-2"> </div> <div id="filling" class="h-60 text-center"> <div class="sample"> <img width="270" height="270" src="my_img.jpg"> <p>coding</p> </div> <div class="sample"> <img width="270" height="270" src="my_img.jpg"> <p>coding</p> </div> <div class="sample"> <img width="270" height="270" src="my_img.jpg"> <p>coding</p> </div> </div> </div> #filling{ display: flex; flex-direction: column; overflow-y: scroll; max-height: 50%; } html { height: 100% } body { height: 100%; } #my-container { height: 100%; }是一个日志表。它用于跟踪在不同时间执行的非常不同的动作（例如温度测量，关门，打开电源开关等）。

我使用以下查询来获取有趣的数据：

TelldusActionsPerformed

这给了我一个看起来像这样的结果集

我想优化查询，以仅返回SELECT TelldusActionsPerformed.PerformedTime AS TelldusActionsPerformed_PerformedTime, TelldusUnits.Name AS TelldusUnits_Name, TelldusActionValues.ActionValue AS TelldusActionValues_ActionValue, TelldusActionValueTypes.Name AS TelldusActionValueTypes_Name FROM TelldusActions INNER JOIN TelldusUnits ON TelldusActions.FK_TelldusUnit_Id = TelldusUnits.Id INNER JOIN TelldusActionTypes ON TelldusActions.FK_TelldusActionType_Id = TelldusActionTypes.Id INNER JOIN TelldusActionValues ON TelldusActions.FK_TelldusActionValue_Id = TelldusActionValues.Id INNER JOIN TelldusActionValueTypes ON TelldusActionValues.FK_TelldusActionValueType_Id = TelldusActionValueTypes.Id INNER JOIN TelldusActionsPerformed ON TelldusActionsPerformed.FK_TelldusAction_Id = TelldusActions.Id WHERE TelldusUnits.Name IN ("Grovkök golvtermostat", "Huvudtermostat", "Uterum golvtermostat") AND TelldusActionValueTypes.Name IN ("watt","temp") ORDER BY TelldusActionsPerformed.PerformedTime DESC + TelldusUnits.Name字段的绝对最新（时间）唯一组合：

我相信我需要TelldusActionValueTypes.Name才能获得独特的组合吗？是否可以仅使用SQL将GROUP BY TelldusUnits.Name, TelldusActionValueTypes.Name + TelldusUnits.Name字段的搜索结果限制为最新的唯一组合？怎么样？

编辑1：

如果我开箱即用地运行Murillo先生的脚本（我只添加了FROM_UNIXTIME（），在我的原始问题中忘记了它）：

TelldusActionValueTypes.Name

我得到以下结果集：

SELECT FROM_UNIXTIME(MAX(TelldusActionsPerformed.PerformedTime)) AS TelldusActionsPerformed_PerformedTime, TelldusUnits.Name AS TelldusUnits_Name, TelldusActionValues.ActionValue AS TelldusActionValues_ActionValue, TelldusActionValueTypes.Name AS TelldusActionValueTypes_Name FROM TelldusActions INNER JOIN TelldusUnits ON TelldusActions.FK_TelldusUnit_Id = TelldusUnits.Id INNER JOIN TelldusActionTypes ON TelldusActions.FK_TelldusActionType_Id = TelldusActionTypes.Id INNER JOIN TelldusActionValues ON TelldusActions.FK_TelldusActionValue_Id = TelldusActionValues.Id INNER JOIN TelldusActionValueTypes ON TelldusActionValues.FK_TelldusActionValueType_Id = TelldusActionValueTypes.Id INNER JOIN TelldusActionsPerformed ON TelldusActionsPerformed.FK_TelldusAction_Id = TelldusActions.Id WHERE TelldusUnits.Name IN ("Grovkök golvtermostat", "Huvudtermostat", "Uterum golvtermostat") AND TelldusActionValueTypes.Name IN ("watt","temp") GROUP BY TelldusUnits.Name, TelldusActionValues.ActionValue, TelldusActionValueTypes.Name ORDER BY TelldusActionsPerformed.PerformedTime DESC使我感到困惑。根据{{1}}，该表似乎不是后代吗？（ORDER BY TelldusActionsPerformed.PerformedTime DESC，UNIX时间戳记的数据类型为int（11））

编辑2：

有关Murillo先生的通缉令的下一次更新使我有了更好的选择：

PerformedTime

仍然有一个细节需要注意（根据我的原始问题：我只希望查询返回PerformedTime + SELECT FROM_UNIXTIME(MAX(TelldusActionsPerformed.PerformedTime)) AS TelldusActionsPerformed_PerformedTime, TelldusUnits.Name AS TelldusUnits_Name, TelldusActionValues.ActionValue AS TelldusActionValues_ActionValue, TelldusActionValueTypes.Name AS TelldusActionValueTypes_Name FROM TelldusActions INNER JOIN TelldusUnits ON TelldusActions.FK_TelldusUnit_Id = TelldusUnits.Id INNER JOIN TelldusActionTypes ON TelldusActions.FK_TelldusActionType_Id = TelldusActionTypes.Id INNER JOIN TelldusActionValues ON TelldusActions.FK_TelldusActionValue_Id = TelldusActionValues.Id INNER JOIN TelldusActionValueTypes ON TelldusActionValues.FK_TelldusActionValueType_Id = TelldusActionValueTypes.Id INNER JOIN TelldusActionsPerformed ON TelldusActionsPerformed.FK_TelldusAction_Id = TelldusActions.Id WHERE TelldusUnits.Name IN ("Grovkök golvtermostat", "Huvudtermostat", "Uterum golvtermostat") AND TelldusActionValueTypes.Name IN ("watt","temp") GROUP BY TelldusUnits.Name, TelldusActionValues.ActionValue, TelldusActionValueTypes.Name ORDER BY MAX(TelldusActionsPerformed.PerformedTime) DESC字段的绝对最新（时间）唯一组合。 / p>

Answer 1

是的，如果您想要最新的时间，则需要添加一个GROUP BY子句，而不考虑TelldusActionsPerformed.PerformedTime。请尝试此脚本

Phones$wt <- rowMeans(subset(Phones, select = c(price, users, rating, market, years)), na.rm = TRUE)

Answer 2

有效答案

即使Murillos不能完全回答我的问题，我还是得到了他的真正帮助（我仍然认为这是一个很好的答案）。这是我最后使用的查询，（希望）回答了我的原始问题：

SELECT 
    OrderedResultSet.TelldusActionsPerformed_PerformedTime,
    OrderedResultSet.TelldusUnits_Name,
    OrderedResultSet.TelldusActionValues_ActionValue,
    OrderedResultSet.TelldusActionValueTypes_Name

FROM (
    SELECT
        FROM_UNIXTIME(MAX(TelldusActionsPerformed.PerformedTime)) AS TelldusActionsPerformed_PerformedTime,
        TelldusUnits.Name AS TelldusUnits_Name,
        TelldusActionValues.ActionValue AS TelldusActionValues_ActionValue,
        TelldusActionValueTypes.Name AS TelldusActionValueTypes_Name

    FROM
        TelldusActions
        INNER JOIN TelldusUnits ON TelldusActions.FK_TelldusUnit_Id = TelldusUnits.Id
        INNER JOIN TelldusActionTypes ON TelldusActions.FK_TelldusActionType_Id = TelldusActionTypes.Id
        INNER JOIN TelldusActionValues ON TelldusActions.FK_TelldusActionValue_Id = TelldusActionValues.Id
        INNER JOIN TelldusActionValueTypes ON TelldusActionValues.FK_TelldusActionValueType_Id = TelldusActionValueTypes.Id
        INNER JOIN TelldusActionsPerformed ON TelldusActionsPerformed.FK_TelldusAction_Id = TelldusActions.Id

    WHERE TelldusUnits.Name IN ("Grovkök golvtermostat", "Huvudtermostat", "Uterum golvtermostat")
        AND TelldusActionValueTypes.Name IN ("watt","temp")

    GROUP BY TelldusUnits.Name, TelldusActionValues.ActionValue, TelldusActionValueTypes.Name

    ORDER BY MAX(TelldusActionsPerformed.PerformedTime) DESC
) as OrderedResultSet

GROUP BY OrderedResultSet.TelldusUnits_Name, OrderedResultSet.TelldusActionValueTypes_Name

这给了我最好的结果（最近一次）：

按订单分组

编辑1：

编辑2：

2 个答案:

有效答案