如何在Android Studio中从数据库中随机选择一行?
我目前正在开发一个简单的android问答应用程序 代码如下:如何在Android Studio中从数据库中随机选择一行?,android,sqlite,android-sqlite,Android,Sqlite,Android Sqlite,我目前正在开发一个简单的android问答应用程序 代码如下: 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.SQ
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;
}
}
package com.example.darel.geogame;
导入android.content.ContentValues;
导入android.content.Context;
导入android.database.Cursor;
导入android.database.sqlite.SQLiteDatabase;
导入android.database.sqlite.SQLiteOpenHelper;
导入java.util.ArrayList;
导入java.util.List;
公共类QuizHelper扩展了SQLiteOpenHelper{
私有静态最终int数据库_VERSION=1;
//数据库名称
私有静态最终字符串数据库\u NAME=“mathsone”;
//任务表名称
私有静态最终字符串表_QUEST=“QUEST”;
//任务表列名称
私有静态最终字符串密钥\u ID=“qid”;
私有静态最终字符串KEY_QUES=“question”;
私有静态最终字符串键\u ANSWER=“ANSWER”//正确选项
私有静态最终字符串键\u OPTA=“OPTA”//选项a
私有静态最终字符串键\u OPTB=“OPTB”//选项b
私有静态最终字符串键\u OPTC=“OPTC”//选项c
专用数据库数据库;
公共QuizHelper(上下文){
super(上下文、数据库名称、null、数据库版本);
}
@凌驾
public void onCreate(SQLiteDatabase db){
dbase=db;
String sql=“创建不存在的表格”+表格任务+”(“
+密钥ID+“整数主键自动递增”+“密钥”
+“文本,”+按键+答案+“文本,”+按键+选项+文本,”
+按键“OPTB+”文本“+按键“OPTC+”文本)”;
execSQL(sql);
添加问题();
//db.close();
}
私人问题{
问题q1=新问题(“5+2=?”、“7”、“8”、“6”、“7”);
这个问题(q1);
问题q2=新问题(“2+18=?”、“18”、“19”、“20”、“20”);
这个问题(q2);
问题q3=新问题(“10-3=?”、“6”、“7”、“8”、“7”);
这个问题(第三季度);
问题q4=新问题(“5+7=?”、“12”、“13”、“14”、“12”);
这个问题(第四季度);
问题q5=新问题(“3-1=?”、“1”、“3”、“2”、“2”);
这个问题(q5);
问题q6=新问题(“0+1=?”、“1”、“0”、“10”、“1”);
这个问题(q6);
问题q7=新问题(“9-9=?”、“0”、“9”、“1”、“0”);
这个问题(q7);
问题q8=新问题(“3+6=?”、“8”、“7”、“9”、“9”);
这个问题(q8);
问题q9=新问题(“1+5=?”、“6”、“7”、“5”、“6”);
这个问题(q9);
问题q10=新问题(“7-5=?”、“3”、“2”、“6”、“2”);
本.补充质询(q10);
问题q11=新问题(“7-2=?”、“7”、“6”、“5”、“5”);
本问题(q11);
问题q12=新问题(“3+5=?”、“8”、“7”、“5”、“8”);
本条问题(q12);
问题q13=新问题(“0+6=?”、“7”、“6”、“5”、“6”);
本问题(第13题);
问题q14=新问题(“12-10=?”、“1”、“2”、“3”、“2”);
本.补充质询(问题14);
问题15=新问题(“12+2=?”、“14”、“15”、“16”、“14”);
本.补充质询(第15题);
问题16=新问题(“2-1=?”、“2”、“1”、“0”、“1”);
本.补充质询(第16题);
问题17=新问题(“6-6=?”、“6”、“12”、“0”、“0”);
本.补充质询(第17题);
问题q18=新问题(“5-1=?”、“4”、“3”、“2”、“4”);
本.补充质询(第18题);
问题19=新问题(“4+2=?”、“6”、“7”、“5”、“6”);
本.补充质询(第19题);
问题q20=新问题(“5+1=?”、“6”、“7”、“5”、“6”);
这个问题(q20);
问题q21=新问题(“5-4=?”、“5”、“4”、“1”、“1”);
这个问题(问题21);
//结束
}
@凌驾
public void onUpgrade(SQLiteDatabase db、intoldv、intnewv){
//删除旧表(如果存在)
db.execSQL(“如果存在删除表”+表任务);
//再次创建表
onCreate(db);
}
//添加新问题
公共问题(问题探索){
//SQLiteDatabase db=this.getWritableDatabase();
ContentValues=新的ContentValues();
value.put(KEY_QUES,quest.getQUESTION());
value.put(KEY_ANSWER,quest.getANSWER());
value.put(KEY_OPTA,quest.getOPTA());
value.put(KEY_OPTB,quest.getOPTB());
value.put(KEY_OPTC,quest.getOPTC());
//插入行
insert(TABLE_QUEST,null,value);
}
公共列表getAllQuestions(){
List quesList=new ArrayList();
//选择所有查询
String selectQuery=“SELECT*FROM”+表格任务;
dbase=this.getReadableDatabase();
Cursor Cursor=dbase.rawQuery(selectQuery,null);
//循环遍历所有行并添加到列表
if(cursor.moveToFirst()){
做{
问题探索=新问题();
setID(cursor.getInt(0));
setquest.setQUESTION(cursor.getString(1));
setANSWER(cursor.getString(2));
setOPTA(cursor.getString(3));
setOPTB(cursor.getString(4));
setOPTC(cursor.getString(5));
添加(任务);
}while(cursor.moveToNext());
}
//返回任务列表
返回任务列表;
}
}
根据上述代码,应用程序将按照编写代码的顺序列出问题。我希望应用程序随机选择一个问题,而不是按顺序,而不重复
有人能帮我吗?
根据上面的代码,应用程序正在按照编写的代码的顺序列出问题。
错误
您从未被授予从表中获取行的顺序。这就是为什么存在ORDER BY子句的原因 除了它的各种修饰符(
ASC
,DESC
)之外,您还可以使用RANDOM()
String selectQuery = "SELECT * FROM " + TABLE_QUEST;
String selectQuery = "SELECT * FROM " + TABLE_QUEST + " ORDER BY RANDOM()";
String selectQuery = "SELECT * FROM " + TABLE_QUEST + " ORDER BY RANDOM() LIMIT 1";