executenonquery方法异常

Question

protected void Button1_Click(object sender, EventArgs e)
    {
        string connectstring = @"server=CSDN-3F5C293478\SQLEXPRESS;database=website;integrated security=true;";
        SqlConnection thisconnection = new SqlConnection(connectstring);
        if (TextBox1.Text == "" || TextBox2.Text == "")
        {
            Response.Write("<script>alert('用户名或者密码不能为空')</script>");
        }
        else
        {
            try
            {
                string sql = "insert into dbo.User (UserName,UserId,Email) values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "')"; 
                SqlCommand cmd = new SqlCommand(sql, thisconnection);
                thisconnection.Open();
                cmd.ExecuteNonQuery();
                Response.Write("<script>windows.location.href='Index.aspx';alert('注册成功');</script>");
            }
            catch(SqlException ee)
            {
                Response.Write(ee.Message);
                //Response.Write("<script>alert('数据库读取错误,请重新输入')</script>");
            }
            finally
            {
                thisconnection.Close();
            }
        }
    }
这是asp.net注册登录时的注册按钮的处理事件,连接数据库没有问题。但是当到了红色的这行时,捕捉到了异常,说是User附近有语法错误,一直不能往数据库里面添加记录,我检查了命令没发现有错误啊？这到底是怎么回事？

Answer 1

 string sql = "insert into dbo.[User] (UserName,UserId,Email) values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "')";