如何查找数据库记录是否存在

在将记录写入文件之前，我试图查看表中是否存在记录，但我一直收到错误

string InformationCheck = "Select FName,LName from Customer where FName ='" + this.f_Name.Text + "' and LName = '" + l_Name.Text + "'";
OleDbCommand InfoCheck = new OleDbCommand(InformationCheck, conn);
String strResult = String.Empty;
try
{
    conn.Open();
    strResult = (String)InfoCheck.ExecuteScalar();
    if (strResult.Length == 0)
    {
        MessageBox.Show("Dose Not Exist");
        AddInfo.ExecuteReader();
        conn.Close();
        this.Hide();
        f1.Show();
    }
    else
    {
        MessageBox.Show("Exists");
    }                    
}
catch (Exception ex)
{
    MessageBox.Show("" + ex + "");
}