当我使用C#在数据库中有相同的记录时，返回false

using System;
using System.Data.SqlClient;

public class DatabaseHelper
{
    private string connectionString = "your_connection_string_here";

    public bool IsUsernameExists(string username)
    {
        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            connection.Open();
            string query = "SELECT COUNT(*) FROM Users WHERE Username = @Username";
            using (SqlCommand command = new SqlCommand(query, connection))
            {
                command.Parameters.AddWithValue("@Username", username);
                int count = (int)command.ExecuteScalar();
                return count > 0;
            }
        }
    }
}

class Program
{
    static void Main()
    {
        DatabaseHelper dbHelper = new DatabaseHelper();
        string usernameToCheck = "exampleUser";
        bool exists = dbHelper.IsUsernameExists(usernameToCheck);
        Console.WriteLine($"Username '{usernameToCheck}' exists: {exists}");
    }
}