在SQLite Android中计算列的总和

Question

我需要计算Column的Sum值.为此我使用以下查询.但是当我单击按钮进行计算时应用程序崩溃了.

Cursor cur = db.rawQuery("SELECT SUM " + (DbHelper.CART_TOTAL) + " FROM " + DbHelper.CART_TABLE, null);
if (cur.moveToFirst()) {
       Log.e("Net Total", cur.getInt(0) + "");
       return cur.getInt(0);
         }
        return 0;

Logcat错误:

      android.database.sqlite.SQLiteException:
     no such column: SUM (code 1): , 
while compiling: SELECT SUM cart_total FROM cart_table
                                                               at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
                                                               at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:882)
                                                               at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:493)
                                                               at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
                                                               at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
                                                               at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
                                                               at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
                                                               at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1314)
                                                               at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1253)
                                                               at com.insideglobe.restaurant.Db.DbUtil.calculateNetTotal(DbUtil.java:276)
                                                               at com.insideglobe.restaurant.Adapter.MyCartAdapter$1.UpdateCart(MyCartAdapter.java:104)
                                                               at com.insideglobe.restaurant.Adapter.MyCartAdapter$1.onClick(MyCartAdapter.java:91)
                                                               at android.view.View.performClick(View.java:4084)
                                                               at android.view.View$PerformClick.run(View.java:16987)
                                                               at android.os.Handler.handleCallback(Handler.java:615)
                                                               at android.os.Handler.dispatchMessage(Handler.java:92)
                                                               at android.os.Looper.loop(Looper.java:137)
                                                               at android.app.ActivityThread.main(ActivityThread.java:4794)
                                                               at java.lang.reflect.Method.invokeNative(Native Method)
                                                               at java.lang.reflect.Method.invoke(Method.java:511)
                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)

Answer 1

正确的方式

 Cursor cursor = db.rawQuery("SELECT SUM(" + DbHelper.CART_TOTAL + ") as Total FROM " + DbHelper.CART_TABLE, null);

 if (cur.moveToFirst()) {

 int total = cursor.getInt(cursor.getColumnIndex("Total"));// get final total

Answer 2

您缺少圆括号。您的查询应该是。

Cursor cur = db.rawQuery("SELECT SUM(" + (DbHelper.CART_TOTAL) + ") FROM " + DbHelper.CART_TABLE, null);