Search (Filter) record between two Month range using C# in ASP.Net

Hi

i want to ask how to make a range data between selected month.

Example (2 -5) month to search data about my staff leave data.

C#

public partial class Op_UserApplyLeaveList : System.Web.UI.Page
{ 
    protected void ibSearch_Click(object sender, ImageClickEventArgs e)
    {
        string message,
        id = Session["ID"].ToString();

        if (ddlSearch.SelectedIndex == 0)
        {
            if (Regex.IsMatch(tbSearch.Text, "[0-9]"))
            {
                sqlUsers.SelectCommand = "SELECT a.leaveId , p.Id, p.Name, a.start, a.end, a.total, a.dateapply, a.Type, a.Status " +
                " FROM  profile as p INNER JOIN " +
                " leaveapp as a On a.Id = p.Id " +
                " Where a.leaveId='" + tbSearch.Text.Trim() + "' " +
                " ORDER BY  a.leaveId DESC";

                gvTranList.DataBind();
            }
            else
            {
                message = "Please enter ID number!";

                string returnUrl = "UserApplyLeaveList.aspx";

                ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", "<script type = 'text/javascript'>" +
            }
        }
        if (ddlSearch.SelectedIndex == 1)
        {
            if (Regex.IsMatch(tbSearch.Text, "[0-9]"))
            {
                sqlUsers.SelectCommand = "SELECT a.leaveId , p.Id, p.Name, a.start, a.end, a.total, a.dateapply, a.Type, a.Status " +
                " FROM  profile as p INNER JOIN " +
                " leaveapp as a On a.Id = p.Id " +
                " Where p.Id='" + tbSearch.Text.Trim() + "' " +
                " ORDER BY  a.leaveId DESC";

                gvTranList.DataBind();
            }
            else
            {
                message = "Please enter Staf I/C!";

                string returnUrl = "UserApplyLeaveList.aspx";

                ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", "<script type = 'text/javascript'>" +
            }
        }
        if (ddlSearch.SelectedIndex == 2)
        {
            if (Regex.IsMatch(tbSearch.Text, "[0-9]"))
            {
                sqlUsers.SelectCommand = "SELECT a.leaveId , p.Id, p.Name, a.start, a.end, a.total, a.dateapply, a.Type, a.Status " +
                " FROM  profile as p INNER JOIN " +
                " leaveapp as a On a.Id = p.Id " +
                " Where Year(a.start) >=  '" + tbSearch.Text.Trim() + "' " +
                " and Year(a.end) <= '" + tbSearch.Text.Trim() + "' " +
                " ORDER BY  a.start DESC";

                gvTranList.DataBind();
            }
            else
            {
                message = "Please enter year!";

                string returnUrl = "UserApplyLeaveList.aspx";

                ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", "<script type = 'text/javascript'>" +
            }
        }
        if (ddlSearch.SelectedIndex == 3)
        {
            if (tbSearch.Text != "")
            {
                sqlUsers.SelectCommand = "SELECT a.leaveId , p.Id, p.Name, a.start, a.end, a.total, a.dateapply, a.Type, a.Status " +
                " FROM  profile as p INNER JOIN " +
                " leaveapp as a On a.Id = p.Id " +
                " Where Month(a.start) >=  '" + tbSearch.Text.Trim() + "' " +
                " and Month(a.end) <= '" + tbSearch.Text.Trim() + "' " +
                " ORDER BY  a.start DESC";

                gvTranList.DataBind();
            }
            else
            {
                message = "Please enter month!";

                string returnUrl = "UserApplyLeaveList.aspx";

                ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", "<script type = 'text/javascript'>" +
            }
        }

        if (ddlSearch.SelectedIndex == 4)
        {
            if (tbSearch.Text != "")
            {
                sqlUsers.SelectCommand = "SELECT a.leaveId , p.Id, p.Name, a.start, a.end, a.total, a.dateapply, a.Type, a.Status " +
                " FROM  profile as p INNER JOIN " +
                " leaveapp as a On a.Id = p.Id " +
                " Where a.Type='" + tbSearch.Text.Trim() + "' " +
                " ORDER BY  a.leaveId DESC";

                gvTranList.DataBind();
            }
            else
            {
                message = "Please enter Type Leave!";

                string returnUrl = "UserApplyLeaveList.aspx";

                ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", "<script type = 'text/javascript'>" +
            }
        }
    }