Room/SQLite 在一个查询中返回两个不同的结果

Question

所以我有以下查询：

//returns min max value my odomoter field must have
@Query("SELECT MAX(odometer) FROM MaintenanceRecord WHERE vehicleId = :maintenanceVehicleId AND " +
        "maintenanceTs < :dateAsLong")
Maybe<Float> getMinAllowedOdometer(long dateAsLong, int maintenanceVehicleId);


//returns the max value my odometer field is allowed to have 
@Query("SELECT MIN(odometer) FROM MaintenanceRecord WHERE vehicleId = :maintenanceVehicleId AND " +
        "CAST(strftime('%s',DATE(maintenanceTs/1000,'unixepoch'))  AS  integer) > " +
        "CAST(strftime('%s',DATE(:dateAsLong/1000,'unixepoch')) AS integer)")
Maybe<Float> getMaxAllowedOdometer(long dateAsLong,int maintenanceVehicleId);

一个函数 returns odometer 列必须具有的最小值，另一个查询 returns odometer 列允许具有的最大值.

问题是 BOTH 函数是依次执行的，因为我需要订阅这两个函数。老实说，这是不好的做法。

我可以将这两个查询放在一个查询中，然后 return Maybe<Float, Float> 作为结果吗？我的另一个解决方案是运行这些功能同步；而不是 Maybe<Float>, 我会直接 return Float.

Answer 1

您可以使用条件聚合在单个查询中获取两列：

SELECT MAX(CASE WHEN maintenanceTs < :dateAsLong THEN odometer END) AS max_odometer,
       MIN(CASE WHEN CAST(strftime('%s', DATE(maintenanceTs / 1000, 'unixepoch')) AS INTEGER) > CAST(strftime('%s', DATE(:dateAsLong / 1000,'unixepoch')) AS INTEGER) THEN odometer END) AS min_odometer
FROM MaintenanceRecord 
WHERE vehicleId = :maintenanceVehicleId;

Room/SQLite 在一个查询中返回两个不同的结果

Room/SQLite returning two different results in one query

sqlite

android

android-sqlite

conditional-aggregation

android-room