从表SQLite中检索多个特定列的数据

Question

我试图从SQLite中一个表的多个特定列中检索数据，但下面的代码不确定为什么，而是从两个不同的列中获取数据，而是从我的方法中的第一列(即“支出”表的“预算”列)获取数据：

        String temp_category = "budget";
        Cursor latestamount = myDb.getLatestAmount(id, temp_category);
        if (latestamount.getCount() == 0) {
            Toast.makeText(AddExpenses.this, "No amount found !", Toast.LENGTH_LONG).show();
        } else {
            latestamount.moveToFirst();
            amountfromdb_budget = latestamount.getDouble(0);
        }

        temp_category = "foodndrinks";
        myDb.getLatestAmount(id, temp_category);
        if (latestamount.getCount() == 0) {
            Toast.makeText(AddExpenses.this, "No amount found !", Toast.LENGTH_LONG).show();
        } else {
            latestamount.moveToFirst();
            amountfromdb_foodndrinks = latestamount.getDouble(0);
        }

使用上面的代码，我的"amountfromdb_budget“和"amountfromdb_foodndrinks”将与amountfromdb_foodndrinks列中的值一起插入。我的目标是将“预算”列中的值检索为"amountfromdb_budget“，将”食品饮料“列中的值检索为"amountfromdb_foodndrinks”。

下面是我DatabaseHelper类中的“DatabaseHelper”方法：

    public Cursor getLatestAmount(String id, String category) {
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor latestamount = db.rawQuery("SELECT "+category+" FROM spendings WHERE id =" +id , null);
        return latestamount;
    }

我的“花销”表的结构如下：

    private static final String SPENDING_TABLE = "spendings";
    private static final String ID_SPENDING = "id";
    private static final String BUDGET = "budget";
    private static final String TOTAL_EXPENSES = "total_expenses";
    private static final String FOODNDRINKS = "foodndrinks";
    private static final String TRAVEL = "travel";
    private static final String SHOPPING = "shopping";
    private static final String ENTERTAINMENT = "entertainment";
    private static final String OTHERS = "others";
    private static final String BALANCE = "balance";

Answer 1

当您获得饮料中的食物数量时，您并没有覆盖光标。因此，您仍然在使用预算光标。因此，将结果从getLatestAmount保存到latestamount。

change

myDb.getLatestAmount(id, temp_category);

到

latestamount = myDb.getLatestAmount(id, temp_category);

，所以您的代码应该类似于这个

String temp_category = "budget";
Cursor latestamount = myDb.getLatestAmount(id, temp_category); 
if (latestamount.getCount() == 0) { 
    Toast.makeText(AddExpenses.this, "No amount found !", Toast.LENGTH_LONG).show(); 
} else {
    latestamount.moveToFirst();
    amountfromdb_budget = latestamount.getDouble(0);
} 

temp_category = "foodndrinks";
// the line below is what you needed to change
latestamount = myDb.getLatestAmount(id, temp_category); 
if (latestamount.getCount() == 0) { 
    Toast.makeText(AddExpenses.this, "No amount found !", Toast.LENGTH_LONG).show(); 
} else { 
    latestamount.moveToFirst();
    amountfromdb_foodndrinks = latestamount.getDouble(0);
}