Search GridView using multiple comma separated fields in ASP.Net

This Way:

HTML:

<div>
        <asp:TextBox ID="txtId" runat="server" />
        <asp:Button Text="Search" OnClick="Search" runat="server" />
        <asp:GridView ID="gvEmployees" runat="server">
        </asp:GridView>
    </div>

C#:

private void WhereCondition()
    {
        string id = txtId.Text.Trim();
        string[] employeesId = id.Split(',');
        string condition = string.Empty;
        foreach (string item in employeesId)
        {
            condition += item + ",";
        }

        string final = condition.Substring(0, condition.Length - 1);
        this.GetEmployees(final);
    }

    private void GetEmployees(string condition)
    {
        string constr = ConfigurationManager.ConnectionStrings["constr2"].ConnectionString;
        string sqlStatment = "SELECT LastName,Country FROM Employees WHERE EmployeeID IN(" + condition + ")";
        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlCommand cmd = new SqlCommand(sqlStatment, con))
            {
                using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                {
                    DataSet ds = new DataSet();
                    da.Fill(ds);
                    this.gvEmployees.DataSource = ds;
                    this.gvEmployees.DataBind();
                }
            }
        }
    }

    protected void Search(object sender, EventArgs e)
    {
        this.WhereCondition();
    }