在 Android 中将 MySql 查询转换为 SQL Room 查询 - kotlin

Posted 2023-04-19

【中文标题】在 Android 中将 MySql 查询转换为 SQL Room 查询 - kotlin

【英文标题】：Converting MySql Query to SQL Room query in Android - kotlin

【发布时间】：2021-08-24 14:01:24

【问题描述】：

我刚刚从后端获得了以下 mysql 查询。 我必须使用 android 中的 Room 数据库在本地管理这些东西。

所以，后端的查询如下：

Select DATE_FORMAT(timeStamp ,'%d-%b') AS date, DATE_FORMAT(timeStamp ,'%d') AS dateNumber, 
ROUND(AVG(IF(stateOfCharge IS NULL, 0, stateOfCharge)), 2) AS chargeOverTime, 
ROUND(AVG(IF(temperature IS NULL, 0, temperature)), 2) AS temperature, 
ROUND(AVG(IF(current IS NULL, 0, current)), 2) AS averageChargeDischarge 
from batteryDetails 
where name="VERNE000003"
and timeStamp between "2021-03-11 11:40:29" AND "2021-03-12 23:40:29"
Group by DATE_FORMAT(timeStamp ,"%Y-%m-%d") ORDER BY timeStamp;

我尝试购买转换如下：

@Query("SELECT datetime(timeStamp ,'%d-%b') AS date, " +
        "datetime(timeStamp ,'%d') AS dateNumber, " +
        "ROUND(AVG(if(stateOfCharge IS NULL, 0, stateOfCharge)), 2) AS chargeOverTime, " +
        "ROUND(AVG(if(temperature IS NULL, 0, temperature)), 2) AS temperature, " +
        "ROUND(AVG(if(current IS NULL, 0, current)), 2) AS averageChargeDischarge " +
        "FROM " + DatabaseConstant.mUserBatteryDetailsTable +
        " WHERE name= :batteryId and timeStamp between :startDate AND :endDate " +
        "GROUP BY datetime(timeStamp ,'%Y-%m-%d') ORDER BY timeStamp")
suspend fun getHistoryData(batteryId: String, startDate: String, endDate: String): List<BatteryDetails>?

但出现以下错误：

错误：查询有问题：[SQLITE_ERROR] SQL 错误或 缺少数据库（没有这样的功能：如果） 公共抽象 java.lang.Object getHistoryData(@org.jetbrains.annotations.NotNull()

【问题讨论】：

用 CASE 替换 IF()。

@Akina 谢谢妈妈，现在得到：“SQL 错误或缺少数据库（靠近“）”：语法错误）“请。指导。

IF(A,B,C) => CASE WHEN A THEN B ELSE C END。但在您的情况下，IF(column IS NULL, 0, column) 可以替换为COALESCE(column, 0)。

IF(stateOfCharge IS NULL, 0, stateOfCharge) 在任何数据库（Access 除外）中的等价物是COALESCE(stateOfCharge, 0)

【参考方案1】：

查询解决如下：

 @Query("Select strftime('%d %m',datetime(timeStamp, 'unixepoch')) as dates, " +
        "strftime('%d', datetime(timeStamp, 'unixepoch')) as dateNumber, " +
        "round(avg(coalesce( stateOfCharge,0))) as chargeOverTime, " +
        "ROUND(AVG(coalesce( avgTemperature,0))) as avgTemperature, " +
        "ROUND(AVG(coalesce(current,0))) as averageChargeDischarge " +
        "FROM " + DatabaseConstant.mUserBatteryDetailsTable +
        " WHERE name= :batteryId and timeStamp between :startDate AND :endDate " +
        "Group by datetime(timeStamp ,'%Y-%m-%d') ORDER BY timeStamp")