Question

我创建了一个数据库帮助器类，我在其中编写了一个选择查询，如下所示：

//select statement
        public String select(String question_id) {

        SQLiteDatabase db = this.getWritableDatabase(); 


        String sql = "SELECT answer FROM answers WHERE _id="+question_id;
         Log.i("select: ",sql);

        db.close();
        return sql;

}

这就是我从活动中调用select方法的方法：

//select statement to retrive previous answer from database
                DataBaseHelper db = new DataBaseHelper(ExamActivity.this);
                ContentValues values = new ContentValues();
                try {
                 db.createDataBase();
                 chk_content = db.select(question_sr_no.getText().toString()); 

                } catch (IOException e1) {
                 e1.printStackTrace();
                  }
                db.close();

但 logcat 输出是：

SELECT answer FROM answers WHERE _id=1.

为什么查询不返回结果，而是返回查询字符串？

提前致谢！

Answer 1

您忘记使用db.rawQuery执行查询。将您的方法更改为：

public String select(String question_id) {
   SQLiteDatabase db = this.getWritableDatabase(); 
   String str_answer="";
   String sql = "SELECT answer FROM answers WHERE _id="+question_id;
   Log.i("select: ",sql);
   Cursor cursor = db.rawQuery(sql, null); //<< execute here 
   cursor.moveToFirst();
   if (cursor.getCount()>0) {
      str_answer=cursor.getString(cursor.getColumnIndex("answer");
    }
  return str_answer;
}

Answer 2

您只是在记录，而不是在调用query method。

Answer 3

您的select方法只创建一个字符串并返回该字符串。看看你自己的代码。

 //select statement
    public String select(String question_id) {

    SQLiteDatabase db = this.getWritableDatabase(); 

    String sql = "SELECT answer FROM answers WHERE _id="+question_id; //you return this. 
     Log.i("select: ",sql);

    db.close();
    return sql;

}

我猜你所追求的是实际查询数据库，而不仅是打开它并再次关闭它。

SQLite选择查询不从表中返回所需的值

3 个答案: