滥用聚合函数 MAX()

Question

我想要警报 table 中列 ignition_status 的 最新非空 值。

我有列 unix_time，它是 Unix 时间戳中的时间，所以最大 unix_time 列值，最新的是条目。

下面是我的代码

cursor = dbUtilsObj.query(Alert.TABLE_NAME, new String[] { alertType_COLUMN }, " MAX(" + Alert.Columns.KEY_ALERT_UNIX_TIME
                + ")" + AND + Alert.Columns.KEY_MACHINE_TELE_DEVICE_NO + EQUALS + AND + alertType_COLUMN + IS_NOT_NULL,
                new String[] { String.valueOf(teleDevieNo) }, null, null, Alert.Columns.KEY_ALERT_UNIX_TIME);

获取错误

(1) misuse of aggregate function MAX()
: android.database.sqlite.SQLiteException: misuse of aggregate function MAX() (code 1): , while compiling: SELECT ignition_status FROM alert WHERE  MAX(unix_time) and tele_device_no = ?  and ignition_status IS NOT NULL  ORDER BY unix_time
at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:1113)
at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:686)
at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1420)
at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1267)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1138)
at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1306)
at com.jd.database.DBUtils.query(DBUtils.java:473)
at com.jd.database.AlertDBUtils.getLatestNotNullValueForType_COLUMN_ByTeleDeviceNo(AlertDBUtils.java:161)
at com.jd.sms.SMSIntentService.parseE1_VehicleMovemenEvent(SMSIntentService.java:158)
at com.jd.sms.SMSIntentService.parseMsgAndInputInDb(SMSIntentService.java:122)
at com.jd.sms.SMSIntentService.processMessage(SMSIntentService.java:97)
at com.jd.sms.SMSIntentService.procassRequest(SMSIntentService.java:71)
at com.jd.sms.SMSIntentService.onHandleIntent(SMSIntentService.java:39)
at android.app.IntentService$ServiceHandler.handleMessage(IntentService.java:65)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:176)
at android.os.HandlerThread.run(HandlerThread.java:60)
android.database.sqlite.SQLiteException: misuse of aggregate function MAX() (code 1): , while compiling: SELECT ignition_status FROM alert WHERE  MAX(unix_time) and tele_device_no = ?  and ignition_status IS NOT NULL  ORDER BY unix_time
  at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:1113)

简而言之，我正在尝试查询 SELECT ignition_status FROM alert WHERE MAX(unix_time) and tele_device_no = ? and ignition_status IS NOT NULL ORDER BY unix_time

那么上面的dbUtilsObj.query()方法应该怎么走呢？至少请告诉我正确的原始查询。

Answer 1

您不能在选择中使用 MAX() 这样的聚合函数。

改为考虑以下内容：

ORDER BY unixtime DESC 将与您的选择匹配的结果排在最前面。
LIMIT 1 仅 return 第一个结果，即最新的。

Answer 2

在 WHERE CLAUSE 中使用 MAX() 函数肯定是可以的，我在下面 it.like 亲自测试过

SELECT ignition_status FROM alert
where 
unix_time=(Select MAX(unix_time) from alert)
and tele_device_no = ?  and ignition_status IS NOT NULL  ORDER BY unix_time

滥用聚合函数 MAX()

Misuse of aggregate function MAX()

android

sqlite

max

aggregate-functions

select-query