Question

我有一个高分的游戏，我试图删除最低分。除了我的应用程序在调用deleteProduct（）方法时崩溃，一切正常。 Logcat说这是一个语法错误，但我真的不知道出了什么问题，因为这是我第一个使用SQLite的应用程序。

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 if((!(DatabaseUtils.queryNumEntries(db, TABLE_PRODUCTS) <= 4)) /*&&  new score is a highscore */){
        //how to insert new high score into correct spot and delete last high score
        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 " + TABLE_PRODUCTS + " WHERE " + COLUMN_PRODUCTNAME + "=\"" + productName + "\";" );
    db.execSQL("DELETE MIN(" + COLUMN_PRODUCTNAME + ") FROM " + TABLE_PRODUCTS +";" );
}


//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");
    //Cursor c = db.rawQuery(query, null);
    //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;

}

}

logcat debuging的主要部分

22688/com.example.emilythacker.myapplication E/SQLiteLog: (1) near "MIN": syntax error
22688/com.example.emilythacker.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                    Process: com.example.emilythacker.myapplication, PID: 22688
                                                                                    android.database.sqlite.SQLiteException: near "MIN": syntax error (code 1): , while compiling: DELETE MIN(productname) FROM products;
                                                                                    #################################################################
                                                                                    Error Code : 1 (SQLITE_ERROR)
                                                                                    Caused By : SQL(query) error or missing database.
                                                                                        (near "MIN": syntax error (code 1): , while compiling: DELETE MIN(productname) FROM products;)
at com.example.emilythacker.myapplication.MyDBHandler.deleteProduct(MyDBHandler.java:76)
                                                                                        at com.example.emilythacker.myapplication.MyDBHandler.addProduct(MyDBHandler.java:53)
                                                                                        at com.example.emilythacker.myapplication.MyDBHandler.addButtonClicked(MyDBHandler.java:62)
                                                                                        at com.example.emilythacker.myapplication.GameScreen.cancel(GameScreen.java:152)
                                                                                        at com.example.emilythacker.myapplication.GameScreen.access$000(GameScreen.java:18)
                                                                                        at com.example.emilythacker.myapplication.GameScreen$1.run(GameScreen.java:34

Answer 1

你的查询结构是错误的。试试这个：

db.execSQL("DELETE FROM products WHERE productname = (SELECT MIN(productname) FROM products)");

而不是：

db.execSQL("DELETE MIN(" + COLUMN_PRODUCTNAME + ") FROM " + TABLE_PRODUCTS +";" );

无法让SQLite删除记录

1 个答案: