Why Can't I update the values of the sqlite database

  public void onClick(View v) {

            if (btn66 == v) {
                ContentValues value = new ContentValues();
                value.put(DBhelper.Amount, txtBudget.getText().toString());
                value.put(DBhelper.Description, txr.getText().toString());

                if(DBhelper.Amount == null)
                {
                    db = helper.getWritableDatabase();
                    db.insert(DBhelper.TABLE2, null, value);
                    db.close();
                    clearfield();
                    Toast.makeText(this, "Budget add Successfully", Toast.LENGTH_LONG).show();
                    fetchData2();
                    Intent i = new Intent(addbudget.this, MainActivity.class);
                    startActivity(i);

                }
                else{
                    db = helper.getWritableDatabase();
                    db.update(DBhelper.TABLE2, value, "_id "+"="+1, null);
                    db.close();

                    fetchData2();
                    Toast.makeText(this, "Update Successfully", Toast.LENGTH_LONG).show();
                    clearfield();
                }
            }
        }

The above one is my code to add and update values to the sqlite database,after I include the Update method in my code,my add function is not working and my update function also not working.Is there any problem with my code,but I didn't get any error message.