Delete department who has no Employees using C# in ASP.Net

Refer below code.

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        ShowData();
    }
}
protected void ShowData()
{
    OleDbConnection connn = new OleDbConnection(@"Provider=Microsoft.ACE.OleDb.12.0;Data Source=C:\Users\sivaranjani\Documents\Database6.accdb");
    connn.Open();
    OleDbCommand cmd = new OleDbCommand("Select DID,DEPID,DEPNAME,MANAGERNAME from tab", connn);
    OleDbDataReader rd = cmd.ExecuteReader();
    DataTable dt = new DataTable();
    dt.Load(rd);
    connn.Close();
    if (dt.Rows.Count > 0)
    {
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
    else
    {
        dt.Rows.Add(dt.NewRow());
        GridView1.DataSource = dt;
        GridView1.DataBind();
        int columncount = GridView1.Rows[0].Cells.Count;
        GridView1.Rows[0].Cells.Clear();
        GridView1.Rows[0].Cells.Add(new TableCell());
        GridView1.Rows[0].Cells[0].ColumnSpan = columncount;
        GridView1.Rows[0].Cells[0].Text = "No Records Found";
    }

}
protected void Button1_Click(object sender, EventArgs e)
{
    foreach (GridViewRow Grow in GridView1.Rows)
    {
        CheckBox chselect = (CheckBox)Grow.FindControl("chkSelect");
        Label lblDEPID = (Label)Grow.FindControl("lblDEPID");
        Label labelDEPNAME = (Label)Grow.FindControl("lblDEPNAME");
        Label labelMANAGERNAME = (Label)Grow.FindControl("lblMANAGERNAME");
        TextBox textDEPNAME = (TextBox)Grow.FindControl("txtDEPNAME");
        TextBox textMANAGERNAME = (TextBox)Grow.FindControl("txtMANAGERNAME");
        labelDEPNAME.Visible = true;
        labelMANAGERNAME.Visible = true;
        textDEPNAME.Visible = false;
        textMANAGERNAME.Visible = false;

        if (chselect.Checked)
        {
            labelDEPNAME.Visible = false;
            labelMANAGERNAME.Visible = false;
            textDEPNAME.Visible = true;
            textMANAGERNAME.Visible = true;
            OleDbConnection connn = new OleDbConnection(@"Provider=Microsoft.ACE.OleDb.12.0;Data Source=C:\Users\sivaranjani\Documents\Database6.accdb");
            connn.Open();
            OleDbCommand cmd = new OleDbCommand("update tab  set DEPNAME='" + textDEPNAME.Text + "',MANAGERNAME='" + textMANAGERNAME.Text + "'where  DEPID='" + Convert.ToInt32(lblDEPID.Text) + "'", connn);
            cmd.ExecuteReader();

            GridView1.EditIndex = -1;
            ShowData();
        }
    }

    ShowData();
}
protected void chkSelect_CheckedChanged(object sender, EventArgs e)
{
    foreach (GridViewRow Grow in GridView1.Rows)
    {
        CheckBox chselect = (CheckBox)Grow.FindControl("chkSelect");
        Label lblDEPID = (Label)Grow.FindControl("lblDEPID");
        Label labelDEPNAME = (Label)Grow.FindControl("lblDEPNAME");
        Label labelMANAGERNAME = (Label)Grow.FindControl("lblMANAGERNAME");
        TextBox textDEPNAME = (TextBox)Grow.FindControl("txtDEPNAME");
        TextBox textMANAGERNAME = (TextBox)Grow.FindControl("txtMANAGERNAME");
        labelDEPNAME.Visible = true;
        labelMANAGERNAME.Visible = true;
        textDEPNAME.Visible = false;
        textMANAGERNAME.Visible = false;
        if (chselect.Checked)
        {
            labelDEPNAME.Visible = false;
            labelMANAGERNAME.Visible = false;
            textDEPNAME.Visible = true;
            textMANAGERNAME.Visible = true;
        }

    }
}
protected void Button2_Click(object sender, EventArgs e)
{
    foreach (GridViewRow Grow in GridView1.Rows)
    {
        CheckBox chselect = (CheckBox)Grow.FindControl("chkSelect");
        Label lblDEPID = (Label)Grow.FindControl("lblDEPID");
        if (chselect.Checked)
        {
            // Check Department exists in Employee table or not.
            if (!this.IsDeptExist(Convert.ToInt32(lblDEPID.Text)))
            {
                OleDbConnection connn = new OleDbConnection(@"Provider=Microsoft.ACE.OleDb.12.0;Data Source=C:\Users\sivaranjani\Documents\Database6.accdb");
                connn.Open();
                OleDbCommand cmd = new OleDbCommand("delete from tab where DEPID='" + Convert.ToInt32(lblDEPID.Text) + "'", connn);
                cmd.ExecuteReader();

                Response.Write("<script>alert('Selected Row Deleted')</script>");
            }
            else
            {
                ClientScript.RegisterClientScriptBlock(this.GetType(), "", "alert('department is having employees so you cant delete the department')", true);
            }
        }

    }
    ShowData();
}
protected bool IsDeptExist(int depid)
{
    OleDbConnection connn = new OleDbConnection(@"Provider=Microsoft.ACE.OleDb.12.0;Data Source=C:\Users\sivaranjani\Documents\Database6.accdb");
    connn.Open();
    OleDbCommand cmd = new OleDbCommand("SELECT * from emp where [DEPID]=@DID", connn);
    cmd.Parameters.AddWithValue("@DID", depid);
    OleDbDataReader rd = cmd.ExecuteReader();
    DataTable tb = new DataTable();
    tb.Load(rd);
    if (tb.Rows.Count > 0)
    {
        return true;
    }
    else
    {
        return false;
    }
}
protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView1.PageIndex = e.NewPageIndex;
    ShowData();
}