android - 游标返回错误值 - sqlite - Android

Question

我正在开发一个短信应用程序，我正在尝试从每次对话中获取最后的短信。

这是我的 SQL 语句:

SELECT MAX(smsTIMESTAMP) AS smsTIMESTAMP,_id, smsID, smsCONID, smsMSG, smsNUM, smsREAD, smsTYPE, smsSHORTMSG, COUNT(*) AS smsNUMMESSAGES FROM sms GROUP BY smsCONID ORDER BY smsTIMESTAMP desc

我在 SQLite Expert 中运行查询并得到正确的响应:

然而，当我在我的应用程序中运行它时，我得到:

这是我的 table

这是我的数据操纵器类:

public class DataManipulator {
    private static final  String DATABASE_NAME = "smsapplication.db";
    private static final int DATABASE_VERSION = 3;
    static final String TABLE_NAME = "sms";
    private static Context context;
    static SQLiteDatabase db;
    private static DataManipulator instance;

    private SQLiteStatement insertStmt;

    private static final String INSERT = "insert or ignore into "
        + TABLE_NAME + " (smsID, smsCONID, smsMSG, smsNUM, smsREAD, smsTIMESTAMP, smsTYPE, smsSHORTMSG) values (?,?,?,?,?,?,?,?)";

    public DataManipulator(Context context) {
        DataManipulator.context = context;
        OpenHelper openHelper = new OpenHelper(DataManipulator.context);
        DataManipulator.db = openHelper.getWritableDatabase();
        this.insertStmt = DataManipulator.db.compileStatement(INSERT);
    }
    public static DataManipulator getInstance(Context mContext)
    {
        if(instance == null)
        {
            instance = new DataManipulator(mContext);
        }
        return instance;
    }
    public long insert(int smsID, int smsCONID, String smsMSG,
            String smsNUM, int smsREAD, long smsTIMESTAMP, String smsTYPE, String smsSHORTMSG) {
        this.insertStmt.bindLong(1, smsID);
        this.insertStmt.bindLong(2, smsCONID);
        this.insertStmt.bindString(3, smsMSG);
        this.insertStmt.bindString(4, smsNUM);
        this.insertStmt.bindLong(5, smsREAD);
        this.insertStmt.bindString(6, String.valueOf(smsTIMESTAMP));
        this.insertStmt.bindString(7, smsTYPE);
        this.insertStmt.bindString(8, smsSHORTMSG);
        return this.insertStmt.executeInsert();
    }

    public void deleteAll() {
        db.delete(TABLE_NAME, null, null);
    }

    public Cursor getLastSmsForAllConversations()
    {
        Cursor cursor = db.query(TABLE_NAME, new String[] {"_id"," MAX(smsTIMESTAMP) AS smsTIMESTAMP ", "smsCONID", "smsNUM", "smsREAD", "smsTYPE","smsSHORTMSG","COUNT(*) AS smsNUMMESSAGES"  },
                null, null, "smsCONID", null, "smsTIMESTAMP desc"); 
        return cursor;
    }
    public Cursor getConversationMessages(int conID)
    {
        Cursor cursor = db.query(TABLE_NAME, new String[] {"_id", "smsID", "smsCONID", "smsMSG", "smsNUM", "smsREAD", "smsTIMESTAMP", "smsTYPE","smsSHORTMSG"  },
                "smsCONID="+conID, null, null, null, "smsTIMESTAMP asc"); 
        return cursor;
    }
    public void printCursor()
    {
        Cursor cursor = db.rawQuery("SELECT MAX(smsTIMESTAMP) AS smsTIMESTAMP,_id, smsID, smsCONID, smsMSG, smsNUM, smsREAD, smsTYPE, smsSHORTMSG, COUNT(*) AS smsNUMMESSAGES FROM sms GROUP BY smsCONID ORDER BY smsTIMESTAMP desc", null);

            //  db.query(TABLE_NAME, new String[] {"_id","smsTIMESTAMP AS smsTIMESTAMP ", "smsCONID", "smsNUM", "smsREAD", "smsTYPE","smsSHORTMSG"  },"smsCONID=40", null, null, null, "smsTIMESTAMP desc");  
        if (cursor.moveToFirst()){
               do{
                  String data ="";
                  data= cursor.getString(cursor.getColumnIndex("smsTIMESTAMP"))+" - " +cursor.getString(cursor.getColumnIndex("smsSHORTMSG"));
                  Log.i("data", data);
               }while(cursor.moveToNext()); 
            }
            cursor.close();
    }

    private static class OpenHelper extends SQLiteOpenHelper {

        OpenHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            db.execSQL("CREATE TABLE " + TABLE_NAME + " (_id INTEGER , smsID INTEGER PRIMARY KEY, smsCONID INTEGER, smsMSG TEXT,smsNUM TEXT, smsREAD INTEGER, smsTIMESTAMP INTEGER, smsTYPE TEXT, smsSHORTMSG TEXT)");
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
            onCreate(db);
        }
         @Override
            public synchronized void close() {

            if (db != null)
                db.close();

            super.close();

            }
    } 
}

Answer 1

当您使用 GROUP BY 时，结果的每一行对应于原始表的多行。这些结果的计算方式有以下三种可能性:

• 具有聚合函数(如 MAX 或 COUNT)的列计算组中所有行的值；
• 出现在 GROUP BY 子句中的列只是取自组中的任何记录(因为组中的所有记录对该列具有相同的值)；
• 其他列是个问题，因为组中的行可能有不同的值。在标准 SQL 中，这样的列是被禁止的； SQLite 允许它们，但只是为您提供组中任意随机行的值，这几乎不是您想要的。从 SQLite 3.7.11 开始，您可以从匹配 MIN 或 MAX 的行中获取值；这是您在 SQLite Exprert 中看到的，但在装有较旧 SQLite 的 Android 上却看不到。

---

要解决您的问题，您必须首先使用 GROUP BY 获取足够的信息来识别您想要的记录:

SELECT smsCONID,                            -- OK: used in GROUP BY
       MAX(smsTIMESTAMP) AS smsTIMESTAMP,   -- OK: aggregate MAX
       COUNT(*) AS smsNUMMESSAGES           -- OK: aggregate COUNT
FROM sms
GROUP BY smsCONID
ORDER BY smsTIMESTAMP DESC

然后，将该结果表与原始 sms 表连接起来，以获取这些记录的其他列:

SELECT *
FROM (SELECT smsCONID,
             MAX(smsTIMESTAMP) AS smsTIMESTAMP,
             COUNT(*) AS smsNUMMESSAGES
      FROM sms
      GROUP BY smsCONID) AS grouped
     JOIN sms
       ON grouped.smsCONID     = sms.smsCONID
      AND grouped.smsTIMESTAMP = sms.smsTIMESTAMP
ORDER BY smsTIMESTAMP DESC