android中sqlite中的Sum查询
android中sqlite中的Sum查询
提问于 2012-10-10 06:15:39
我是java，android和sqlite的新手，对此我很迷茫。我有几个列，分别是_id，description.what，amount( int )，category，我正在尝试获取一个特定类别的金额之和，并将它们存储在int中。我知道我需要提供错误，但它只是给了我强制close.Please帮助
public class TransactionReport extends Activity {
private static SQLiteDatabase db;
Cursor c;
int amount;
DbCrud localDbCrud = new DbCrud(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.report);
localDbCrud.open(); //localDatabase = localDbHelper.getWritableDatabase(); return this;
c.moveToFirst();
do{
c = db.rawQuery("select sum(amount) from transaction_table where category = Salary ;", null);
}while(c.moveToNext());
amount = c.getInt(0);
c.close();
TextView ltxt = (TextView) findViewById(R.id.amt);
ltxt.setText(""+amount);
localDbCrud.close(); //localDatabase.close();
}
}如果详细解释会有帮助，因为我是一个彻头彻尾的菜鸟，我确实试图找到解决方案，但没有事先找到any.Thanks
10-10 03:55:29.828: E/AndroidRuntime(10229): FATAL EXCEPTION: main
10-10 03:55:29.828: E/AndroidRuntime(10229): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.hishighness.budgetracker/com.hishighness.budgetracker.TransactionReport}: java.lang.NullPointerException
10-10 03:55:29.828: E/AndroidRuntime(10229): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
10-10 03:55:29.828: E/AndroidRuntime(10229): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
10-10 03:55:29.828: E/AndroidRuntime(10229): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
10-10 03:55:29.828: E/AndroidRuntime(10229): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
10-10 03:55:29.828: E/AndroidRuntime(10229): at android.os.Handler.dispatchMessage(Handler.java:99)
10-10 03:55:29.828: E/AndroidRuntime(10229): at android.os.Looper.loop(Looper.java:130)
10-10 03:55:29.828: E/AndroidRuntime(10229): at android.app.ActivityThread.main(ActivityThread.java:3687)
10-10 03:55:29.828: E/AndroidRuntime(10229): at java.lang.reflect.Method.invokeNative(Native Method)
10-10 03:55:29.828: E/AndroidRuntime(10229): at java.lang.reflect.Method.invoke(Method.java:507)
10-10 03:55:29.828: E/AndroidRuntime(10229): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
10-10 03:55:29.828: E/AndroidRuntime(10229): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
10-10 03:55:29.828: E/AndroidRuntime(10229): at dalvik.system.NativeStart.main(Native Method)
10-10 03:55:29.828: E/AndroidRuntime(10229): Caused by: java.lang.NullPointerException
10-10 03:55:29.828: E/AndroidRuntime(10229): at com.hishighness.budgetracker.TransactionReport.onCreate(TransactionReport.java:27)
10-10 03:55:29.828: E/AndroidRuntime(10229): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-10 03:55:29.828: E/AndroidRuntime(10229): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
10-10 03:55:29.828: E/AndroidRuntime(10229): ... 11 more这是日志。
回答 2
Stack Overflow用户
回答已采纳
发布于 2012-10-10 06:18:15
添加
我相信你想使用localDBCrud.rawQuery()，而不是db.rawQuery()。
原始
我猜你有一个NullPointerException。这里：
c.moveToFirst();在使用db.rawQuery()初始化c之前，您正在尝试使用它。
这里有更多的逻辑错误：
c.moveToFirst();
do{
c = db.rawQuery("select sum(amount) from transaction_table where category = Salary ;", null);
}while(c.moveToNext());
amount = c.getInt(0);
c.close();试着这样做：
c = db.rawQuery("select sum(amount) from transaction_table where category = Salary ;", null);
if(c.moveToFirst())
amount = c.getInt(0);
else
amount = -1;
c.close();@toadsky也做了很好的观察，也听从了他的建议。
Stack Overflow用户
发布于 2012-10-10 06:18:28
应该用单引号将字符串值括起来。因此，不是：
select sum(amount) from transaction_table where category = Salary ;执行以下操作：
select sum(amount) from transaction_table where category = 'Salary';页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/12809214
复制相关文章
相似问题
腾讯云开发者
