Question

我正在尝试对数据库中的数字进行排序，以打印出游戏的五个高分。问题是，当我尝试排序时，我要么按第一个数字排序，要么将两位数字打印到我的高分。混乱是在deleteProduct（）方法中。

DBHandler类

public class MyDBHandler extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 4;
private static final String DATABASE_NAME = "products.db";
public static final String TABLE_PRODUCTS = "products";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_PRODUCTNAME = "productname";

public MyDBHandler(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
    super(context, DATABASE_NAME, factory, DATABASE_VERSION);
}


@Override
public void onCreate(SQLiteDatabase db) {
    String query = "CREATE TABLE " + TABLE_PRODUCTS + "(" +
            COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
            COLUMN_PRODUCTNAME + " TEXT " +
            ");";
    db.execSQL(query);
}

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

//add a new row to the database
public void addProduct(Products product){

    SQLiteDatabase db = this.getReadableDatabase();
    if(DatabaseUtils.queryNumEntries(db, TABLE_PRODUCTS) <= 4){
        ContentValues values = new ContentValues();
        values.put(COLUMN_PRODUCTNAME, product.get_productname());
        db.insert(TABLE_PRODUCTS, null, values);
        db.close();
    }
    else{
        ContentValues values = new ContentValues();
        values.put(COLUMN_PRODUCTNAME, product.get_productname());
        db.insert(TABLE_PRODUCTS, null, values);
        deleteProduct();
        db.close();
    }
}

//code coming from MainActivity
public void addButtonClicked(String highscore1){
    Products product = new Products(highscore1);
    addProduct(product);
    updateDatabase();
}

//code coming from MainActivity
public void updateDatabase(){
        String dbString = databaseToString();
        MainActivity.productText.setText(dbString);
}

//delete a product from the database
public void deleteProduct(){
    SQLiteDatabase db = getWritableDatabase();
    db.execSQL("DELETE FROM products WHERE _id NOT IN"+
                //only reading first digit of double digit numbers
               //" (SELECT _id FROM products ORDER BY  productname DESC LIMIT 5)");
            //this runs but isnt putting double digit scores into the high score textView
            " (SELECT _id FROM products ORDER BY  length(productname), productname DESC LIMIT 5)");


}


//print out the database as a string
public String databaseToString(){
    String dbString = "";
    SQLiteDatabase db = getWritableDatabase();
    String query = "SELECT * FROM " + TABLE_PRODUCTS + " WHERE 1";


    //Cursor point to location in your results
    Cursor c = db.query(TABLE_PRODUCTS, null, null, null, null, null, COLUMN_PRODUCTNAME +" DESC");
    //Move to the first row in your results
    c.moveToFirst();

    while(!c.isAfterLast()){
        if(c.getString(c.getColumnIndex("productname")) != null){
            dbString += c.getString(c.getColumnIndex("productname"));
            dbString += "\n";
        }
        c.moveToNext();

    }


    db.close();
    return dbString;

}

Answer 1

SELECT _id FROM products ORDER BY productname DESC LIMIT 5

此查询按productname列中的值排序。如果这些值是字符串，则排序顺序由第一个字符定义。

您应该存储数字。

如果您无法更改数据库，请在将值用于排序之前将值转换为数字：

SELECT _id FROM products ORDER BY CAST(productname AS NUMBER) DESC LIMIT 5

无法在SQLite中订购两位数字

1 个答案: