Kann SQLite nicht einen Datensatz löschen

Question

Ich habe ein Spiel mit hohen Punktzahlen und versuche, die niedrigste Punktzahl zu löschen. Alles funktioniert, außer dass meine App abstürzt, wenn meine deleteProduct() -Methode aufgerufen wird. Logcat sagt, dass es ein Syntaxfehler ist, aber ich weiß wirklich nicht, was falsch ist, da dies meine erste Anwendung mit SQLite ist.

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; 

} 

}

Hauptteile logcat debuging

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

Sie abfragen Struktur falsch ist. Versuchen Sie folgendes:

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

statt:

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