将textbox.text与数据库列进行比较以查找匹配的用户名

Question

我正在尝试建立一个应该比较数据库中是否存在用户名的注册系统。

这是我的表

CREATE TABLE [dbo].[Registros] (
[ID_Utilizador]          INT          IDENTITY (1, 1) NOT NULL,
[NomeUtilizador]         VARCHAR (20) NOT NULL,
[PasseUtilizador]        VARCHAR (20) NOT NULL,
[EmailUtilizador]        VARCHAR (50) NOT NULL,
[NomeCompletoUtilizador] VARCHAR (50) NOT NULL,
[PaisUtilizador]         CHAR (10)    NOT NULL,
PRIMARY KEY CLUSTERED ([ID_Utilizador] ASC)
);

这应该验证用户是否存在于“NomeUtilizador”列中的某些原因..但它不适用于

    if (IsPostBack)
    {
        SqlConnection conexao = new SqlConnection(ConfigurationManager.ConnectionStrings["RegistrosConnectionString"].ConnectionString);
        conexao.Open();

        string cmdstr = "SELECT COUNT(*) FROM Registros WHERE NomeUtilizador ='"+TBusername.Text+"'";

        SqlCommand UserExists= new SqlCommand(cmdstr, conexao);

        int temp = Convert.ToInt32(UserExists.ExecuteScalar().ToString());

        conexao.Close();

        if (temp ==1)
        {
            Response.Write(" UsernameAlreadyExists! <br /> choose another ");
        }
    }
}

解决方案

   protected void BTsubmeter_Click(object sender, EventArgs e)
{
    SqlDataReader reader = null;
    SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["RegistrosConnectionString"].ConnectionString);
    conn.Open();
    SqlCommand cmd = new SqlCommand("select * from Table where NomeUtilizador=@NomeUtilizador", conn);
    cmd.Parameters.AddWithValue("@NomeUtilizador", TBusername.Text);
    reader = cmd.ExecuteReader();
    if (reader != null && reader.HasRows)
    {
        //if username is matching 
        Response.Write(" Username Exists! <br />Choose another ");
        conn.Close();
    }
    else
    {
        //if not matching do something
    }

P.S：感谢所有想要帮助并度过愉快的一天的人：）