沒有這樣的列錯誤：如果在db中沒有項目，如何防止這個錯誤？

嗯，我想我的標題說明了...用下面的代碼：沒有這樣的列錯誤：如果在db中沒有項目，如何防止這個錯誤？

public int getCorrectAnswersPrev(int level, String player) { 
     int count = 0; 
     level = level - 1; 
     Cursor c = myDataBase.rawQuery(
       "SELECT COUNT(*) FROM ANSWERS WHERE LEVEL =" + level 
         + " AND ANSWERCORRECT = 1 AND PLAYER=" + player, null); 
     c.moveToFirst(); 
     count = c.getInt(0); 
     c.close(); 
     myDataBase.close(); 

     return count; 

    }

有時玩家根本就沒有回答某些問題，那麼就意味着在一個水平的開始，有沒有具體的項目那裏...我得到這個錯誤，雖然我初始化計數爲0，但我明白它仍然執行查詢並返回錯誤。但有沒有一種方法可以防止這種情況，如果在數據庫中沒有項目？

編輯：

11-16 13:34:30.188: E/AndroidRuntime(10206): FATAL EXCEPTION: main 
11-16 13:34:30.188: E/AndroidRuntime(10206): android.database.sqlite.SQLiteException: no such column: Bog: , while compiling: SELECT COUNT(*) FROM ANSWERS WHERE LEVEL =1 AND ANSWERCORRECT = 1 AND PLAYER=Bog 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.database.sqlite.SQLiteCompiledSql.native_compile(Native Method) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.database.sqlite.SQLiteCompiledSql.compile(SQLiteCompiledSql.java:92) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.database.sqlite.SQLiteCompiledSql.<init>(SQLiteCompiledSql.java:65) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:83) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:49) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:42) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1356) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1324) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at com.hup.game.db.DataBaseHelper.getCorrectAnswers(DataBaseHelper.java:251) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at com.hup.game.LevelSelectorAdapter.getView(LevelSelectorAdapter.java:75) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.widget.AbsListView.obtainView(AbsListView.java:1432) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.widget.GridView.onMeasure(GridView.java:935) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.view.View.measure(View.java:8319) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.widget.LinearLayout.measureVertical(LinearLayout.java:386) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.widget.LinearLayout.onMeasure(LinearLayout.java:309) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.view.View.measure(View.java:8319) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.widget.FrameLayout.onMeasure(FrameLayout.java:250) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.view.View.measure(View.java:8319) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.widget.FrameLayout.onMeasure(FrameLayout.java:250) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.view.View.measure(View.java:8319) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.view.ViewRoot.performTraversals(ViewRoot.java:839) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.view.ViewRoot.handleMessage(ViewRoot.java:1865) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.os.Handler.dispatchMessage(Handler.java:99) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.os.Looper.loop(Looper.java:130) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at android.app.ActivityThread.main(ActivityThread.java:3683) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at java.lang.reflect.Method.invokeNative(Native Method) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at java.lang.reflect.Method.invoke(Method.java:507) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:861) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:619) 
11-16 13:34:30.188: E/AndroidRuntime(10206): at dalvik.system.NativeStart.main(Native Method)

來源

2012-11-16 Matthias Vanb

問題在查詢..請在這裏發表完整的錯誤跟蹤，所以我們可以幫助您更好地 – Cata

Editted我的帖子 –

SELECT COUNT(*) FROM ANSWERS WHERE LEVEL =1 AND ANSWERCORRECT = 1 AND PLAYER=Bog

拋出一個錯誤。

應該

SELECT COUNT(*) FROM ANSWERS WHERE LEVEL =1 AND ANSWERCORRECT = 1 AND PLAYER='Bog'

來源

2012-11-16 12:37:53

事實上，這的確有訣竅！增加Kalai Selvan和@Luis的解決方案也是明智的，還是這不是必要的？ –

如果這是必需的，您也可以添加。 –

@sas：你是正確的傢伙 –

Use "ifnull"

爲如：

Cursor c = myDataBase.rawQuery(select ifnull(max(tm.no),0) as serial_no " 
         + "from table_bun as tb inner join table_mar" 
         + " as tm on tb.id = tm.id " 
         + "where tb.bid = " + bId 
         + " and tb.sid = " + SId 
         + " and tb.eby = '" + UId + "'", null);

來源

2012-11-16 12:32:58

經過player級聯值可能視爲列名，所以不是：

Cursor c = myDataBase.rawQuery(
    "SELECT COUNT(*) FROM ANSWERS WHERE LEVEL =" + level 
    + " AND ANSWERCORRECT = 1 AND PLAYER=" + player, null);

試用參數來做TER值：

Cursor c = myDataBase.rawQuery(
    "SELECT COUNT(*) FROM ANSWERS WHERE LEVEL = ? " + 
    " AND ANSWERCORRECT = 1 AND PLAYER = ?", 
    new String[] { String.valueOf(level), player } 
);

來源

2012-11-16 12:34:00

米哈爾您好，感謝，但我得到了它的工作''之前和之後我的變量... :) –

@MatthiasVanb是的，你可以這樣做，但它很容易[SQL注入]（http://en.wikipedia.org/wiki/SQL_injection）。即使你正在學習這一點，也應該嘗試正確的做法:-)。 –

好的，但我認爲這主要是我會處理edittext字段的情況？或者我錯了？ –

如果沒有記錄，Cursor回報null。

你應該使用moveToFirst()這樣之前測試c == null：

if(c != null){ 
    c.moveToFirst(); 


}

來源

2012-11-16 12:36:26 Luis

沒有這樣的列錯誤：如果在db中沒有項目，如何防止這個錯誤？

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