mysql - 返回左表中的所有行，即使右表中没有记录以及右表中的最大到期日期

Question

提前感谢您帮助我解决这个问题，我是 SQL Server 新手，需要您的专家帮助，我想返回左表中的所有值，即使右表中没有记录以及 MAX(MOT Expiry) 或 MAX(Road)税)到期。

我尝试了此查询，但无法获得所需的结果

    SELECT Vehicle.id,vehicle.registrationMark, vehicle.status, RoadTax.Expiry, MOT.Expiry
    FROM Vehicle
    LEFT JOIN RoadTax ON Vehicle.id = RoadTax.VehicleID
    LEFT JOIN MOT ON Vehicle.id = MOT.VehicleID;

为了清楚地说明这一点，请看这个例子。我想从车辆表中返回所有车辆及其最大 TAX 和 MOT 到期时间。甚至道路税或 MOT 表中也没有车辆记录。

车辆表

    ---------------------------------
    | ID | RegistrationMark | Status |
    ---------------------------------
    |  1 | ABC              | Active |
    |  2 | DEF              | Active |
    |  3 | GHI              | Active |
    ---------------------------------

道路税表

    ------------------------------
    | ID | VehicleID | Expiry     |
    ------------------------------
    |  1 | 1         | 10/10/2013 |
    |  2 | 1         | 10/10/2014 |
    |  3 | 2         | 20/12/2014 |
    ------------------------------

MOT表

    -------------------------------
    | ID | VehicleID | Expiry      |
    -------------------------------
    | 1  | 2         | 25/01/2015  |
    -------------------------------

我想要的结果

    -----------------------------------------------------------
    | ID | RegistrationMark | Status | TaxExpiry  | MOTExpiry  |
    -----------------------------------------------------------
    | 1  | ABC              | Active | 10/10/2014 | NULL       |
    | 2  | DEF              | Active | 20/12/2014 | 25/01/2015 |
    | 3  | GHI              | Active | NULL       | NULL       |
    -----------------------------------------------------------

非常感谢您的帮助。

Answer 1

看来您的查询走在正确的轨道上 - 您只需要添加聚合即可:

SELECT Vehicle.id,vehicle.registrationMark, vehicle.status
, Max(RoadTax.Expiry) as LatestTax_Exp
, Max(MOT.Expiry) as LatestMOT_Exp
FROM Vehicle
LEFT JOIN RoadTax ON Vehicle.id = RoadTax.VehicleID
LEFT JOIN MOT ON Vehicle.id = MOT.VehicleID;
group by vehicle.ID, vehicle.Registrationmark, vehicle.status

或者，如果我误解了您想要的内容并且车辆可以有多个状态或注册，请尝试:

SELECT Vehicle.id,vehicle.registrationMark, vehicle.status
, Max(RoadTax.Expiry) over (partition by Vehicle.ID) as LatestRT_Exp
, Max(MOT.Expiry) over (partition by Vehicle.ID) as LatestMOT_Exp
FROM Vehicle
LEFT JOIN RoadTax ON Vehicle.id = RoadTax.VehicleID
LEFT JOIN MOT ON Vehicle.id = MOT.VehicleID;