从SUM sqlite中减去SUM

Question

我试图得到两列的总和并从第一列中减去第二列（两者都是正值。）

public int getSum(){
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor c = db.rawQuery("SELECT SUM (" + KEY_CREDIT + ") - SUM (" + KEY_DEBIT + ") AS myTotal FROM " + TABLE_DEFAULT_ACCOUNT, null);
        if(c.moveToFirst()) {
            sum = c.getInt(c.getColumnIndex("myTotal"));
        }
        return sum;
    }

由于某种原因它返回0，即使在Credit列中的数据肯定是。现在它应该是27 - 0 = 27

如果我将其作为

运行

// GET SUM
    public int getSum(){
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor c = db.rawQuery("SELECT SUM (" + KEY_CREDIT + ") FROM " + TABLE_DEFAULT_ACCOUNT, null);
        if(c.moveToFirst()) {
            sum = c.getInt(0);
        }
        return sum;
    }

它返回27就好了。

感谢任何帮助！

Answer 1

以下对我有用：

// GET SUM
    public int getSum(){
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor c = db.rawQuery("SELECT SUM(credit), SUM(debit) FROM " + TABLE_DEFAULT_ACCOUNT, null);
        if(c.moveToFirst()) {
            sum = (c.getInt(0) - c.getInt(1));
        }
        return sum;
    }