Android Studioでデータベースからランダムに行を選択するにはどうすればよいですか？

Question

私は現在、簡単なアンドロイドクイズアプリを開発中です。次のように

コードは：

package com.example.darel.geogame; 

import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 

import java.util.ArrayList; 
import java.util.List; 


public class QuizHelper extends SQLiteOpenHelper { 
    private static final int DATABASE_VERSION = 1; 
    // Database Name 
    private static final String DATABASE_NAME = "mathsone"; 
    // tasks table name 
    private static final String TABLE_QUEST = "quest"; 
    // tasks Table Columns names 
    private static final String KEY_ID = "qid"; 
    private static final String KEY_QUES = "question"; 
    private static final String KEY_ANSWER = "answer"; // correct option 
    private static final String KEY_OPTA = "opta"; // option a 
    private static final String KEY_OPTB = "optb"; // option b 
    private static final String KEY_OPTC = "optc"; // option c 
    private SQLiteDatabase dbase; 
    public QuizHelper(Context context) { 
     super(context, DATABASE_NAME, null, DATABASE_VERSION); 
    } 
    @Override 
    public void onCreate(SQLiteDatabase db) { 
     dbase = db; 
     String sql = "CREATE TABLE IF NOT EXISTS " + TABLE_QUEST + " (" 
       + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_QUES 
       + " TEXT, " + KEY_ANSWER + " TEXT, " + KEY_OPTA + " TEXT, " 
       + KEY_OPTB + " TEXT, " + KEY_OPTC + " TEXT)"; 
     db.execSQL(sql); 
     addQuestion(); 
// db.close(); 
    } 
    private void addQuestion() { 
     Question q1 = new Question("5+2 = ?", "7", "8", "6", "7"); 
     this.addQuestion(q1); 
     Question q2 = new Question("2+18 = ?", "18", "19", "20", "20"); 
     this.addQuestion(q2); 
     Question q3 = new Question("10-3 = ?", "6", "7", "8", "7"); 
     this.addQuestion(q3); 
     Question q4 = new Question("5+7 = ?", "12", "13", "14", "12"); 
     this.addQuestion(q4); 
     Question q5 = new Question("3-1 = ?", "1", "3", "2", "2"); 
     this.addQuestion(q5); 
     Question q6 = new Question("0+1 = ?", "1", "0", "10", "1"); 
     this.addQuestion(q6); 
     Question q7 = new Question("9-9 = ?", "0", "9", "1", "0"); 
     this.addQuestion(q7); 
     Question q8 = new Question("3+6 = ?", "8", "7", "9", "9"); 
     this.addQuestion(q8); 
     Question q9 = new Question("1+5 = ?", "6", "7", "5", "6"); 
     this.addQuestion(q9); 
     Question q10 = new Question("7-5 = ?", "3", "2", "6", "2"); 
     this.addQuestion(q10); 
     Question q11 = new Question("7-2 = ?", "7", "6", "5", "5"); 
     this.addQuestion(q11); 
     Question q12 = new Question("3+5 = ?", "8", "7", "5", "8"); 
     this.addQuestion(q12); 
     Question q13 = new Question("0+6 = ?", "7", "6", "5", "6"); 
     this.addQuestion(q13); 
     Question q14 = new Question("12-10 = ?", "1", "2", "3", "2"); 
     this.addQuestion(q14); 
     Question q15 = new Question("12+2 = ?", "14", "15", "16", "14"); 
     this.addQuestion(q15); 
     Question q16 = new Question("2-1 = ?", "2", "1", "0", "1"); 
     this.addQuestion(q16); 
     Question q17 = new Question("6-6 = ?", "6", "12", "0", "0"); 
     this.addQuestion(q17); 
     Question q18 = new Question("5-1 = ?", "4", "3", "2", "4"); 
     this.addQuestion(q18); 
     Question q19 = new Question("4+2 = ?", "6", "7", "5", "6"); 
     this.addQuestion(q19); 
     Question q20 = new Question("5+1 = ?", "6", "7", "5", "6"); 
     this.addQuestion(q20); 
     Question q21 = new Question("5-4 = ?", "5", "4", "1", "1"); 
     this.addQuestion(q21); 
// END 
    } 
    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldV, int newV) { 
// Drop older table if existed 
     db.execSQL("DROP TABLE IF EXISTS " + TABLE_QUEST); 
// Create tables again 
     onCreate(db); 
    } 
    // Adding new question 
    public void addQuestion(Question quest) { 
// SQLiteDatabase db = this.getWritableDatabase(); 
     ContentValues values = new ContentValues(); 
     values.put(KEY_QUES, quest.getQUESTION()); 
     values.put(KEY_ANSWER, quest.getANSWER()); 
     values.put(KEY_OPTA, quest.getOPTA()); 
     values.put(KEY_OPTB, quest.getOPTB()); 
     values.put(KEY_OPTC, quest.getOPTC()); 
// Inserting Row 
     dbase.insert(TABLE_QUEST, null, values); 
    } 
    public List<Question> getAllQuestions() { 
     List<Question> quesList = new ArrayList<Question>(); 
// Select All Query 
     String selectQuery = "SELECT * FROM " + TABLE_QUEST; 
     dbase = this.getReadableDatabase(); 
     Cursor cursor = dbase.rawQuery(selectQuery, null); 
// looping through all rows and adding to list 
     if (cursor.moveToFirst()) { 
      do { 
       Question quest = new Question(); 
       quest.setID(cursor.getInt(0)); 
       quest.setQUESTION(cursor.getString(1)); 
       quest.setANSWER(cursor.getString(2)); 
       quest.setOPTA(cursor.getString(3)); 
       quest.setOPTB(cursor.getString(4)); 
       quest.setOPTC(cursor.getString(5)); 
       quesList.add(quest); 
      } while (cursor.moveToNext()); 
     } 
// return quest list 
     return quesList; 
    } 
} 

上記のコードによれば、アプリが書かれたコードの順に質問をリストされています。
私はアプリを繰り返しなくして順不同で質問を選択したいと思っています。

誰かが私を助けることができますか？

Answer 1

According to the above code, the app is listing the questions in order of the code written.間違った。

テーブルから行をフェッチする順番は決して与えられません。
これは、ORDER BY句が存在する理由です。

さまざまな修飾子（ASC、DESC）に加えて、行セットをシャッフルするRANDOM()を使用することもできます。

したがって、代わりの

String selectQuery = "SELECT * FROM " + TABLE_QUEST; 

使用

String selectQuery = "SELECT * FROM " + TABLE_QUEST + " ORDER BY RANDOM()"; 

あなたは単一質問が必要な場合は、

String selectQuery = "SELECT * FROM " + TABLE_QUEST + " ORDER BY RANDOM() LIMIT 1"; 

を使用することができます。しかし、これはということを許可しません。次にクエリを実行すると、同じ行が再び表示されません。

したがって、私は一度にすべての行をフェッチし、一度に1つの行を消費します。