command更新数据 数据重复而不是覆盖

这是.net写的后台··这一段是更新联系方式的代码，就是一个企业网站的联系方式页面，但每次点提交，数据会添加而不是覆盖，比如code 510990  提交后就变成510990510990 变成重复，请高手知道或者用其他方法·，本人新手，
 protected void Button1_Click(object sender, EventArgs e)
    {
        int intUpdataCount;
        string sqlconnstr = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        SqlConnection sqlconn = new SqlConnection(sqlconnstr);
        SqlCommand sqlcommand = new SqlCommand();
        sqlcommand.Connection = sqlconn;
         = "StoredProcedure1";
         = CommandType.StoredProcedure;
        sqlcommand.Parameters.AddWithValue("@mcid", '1');
        sqlcommand.Parameters.AddWithValue("@address", TextBox1.Text);
        sqlcommand.Parameters.AddWithValue("@phone", TextBox2.Text);
        sqlcommand.Parameters.AddWithValue("@code", TextBox3.Text);
        sqlcommand.Parameters.AddWithValue("@qq", TextBox4.Text);
        sqlcommand.Parameters.AddWithValue("@email", TextBox5.Text);
        try
        {
            sqlconn.Open();
            intUpdataCount = sqlcommand.ExecuteNonQuery();
            if (intUpdataCount > 0)
            {
                Response.Write("<script>alter(\"更新成功\");</script>");
            }
        }   
        finally
        {
            sqlcommand = null;
            sqlconn.Close();
            sqlconn = null;
        }
    }
存储过程
ALTER PROCEDURE dbo.StoredProcedure1
(
@mcid bigint,
@address nvarchar(50),
@phone nvarchar(50),
@code nvarchar(50),
@qq nvarchar(50),
@email nvarchar(50)
)
AS
update Contact set address=@address, phone=@phone, code=@code, qq=@qq, email=@email where mcid=@mcid
RETURN