How to use button click event for database connectivity and enabling java script

        Text="Label">

using System;

using System.Collections;

using System.Configuration;

using System.Data;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Xml.Linq;

using System.Data.SqlClient;

using System.Collections.Specialized;

using System.Collections.Generic;

using System.Text;

public partial class _Default : System.Web.UI.Page

{

    string connStr = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;

    SqlCommand cmd = new SqlCommand();

    SqlConnection con;

    string str;

    protected void Page_Load(object sender, EventArgs e)

    {

        if (!Page.IsPostBack)

            BindGridView();

        totalrecords();

    }

    private void totalrecords()

    {

        con = new SqlConnection(connStr);

        //cmd.Connection = con;

        con.Open();

        str = "select count(*) from employee ";

        SqlCommand cmd = new SqlCommand(str, con);

        int row = (int)cmd.ExecuteScalar();

        Label2.Text = row.ToString();

        con.Close();

    }

    private void BindGridView()

    {

        con = new SqlConnection(connStr);

        cmd.Connection = con;

        cmd.CommandText = "Select * from employee";

        con.Open();

        GridView1.DataSource = cmd.ExecuteReader();

        GridView1.DataBind();

        con.Close();

    }

    private void DeleteRecords(StringCollection sc)

    {

        con = new SqlConnection(connStr);

        StringBuilder sb = new StringBuilder(string.Empty);

        foreach (string item in sc)

        {

            const string sqlStatement = "DELETE FROM employee WHERE EmpId";

            sb.AppendFormat("{0}='{1}'; ", sqlStatement, item);

        }

        try

        {

            con.Open();

            SqlCommand cmd = new SqlCommand(sb.ToString(), con);

            cmd.CommandType = CommandType.Text;

            cmd.ExecuteNonQuery();

        }

        catch (System.Data.SqlClient.SqlException ex)

        {

            string msg = "Deletion Error:";

            msg += ex.Message;

            throw new Exception(msg);

        }

        finally

        {

            con.Close();

        }

    }

    protected void ButtonDelete_Click(object sender, EventArgs e)

    {

        StringCollection sc = new StringCollection();

        string id = string.Empty;

        for (int i = 0; i < GridView1.Rows.Count; i++)

        {

            CheckBox cb = (CheckBox)GridView1.Rows[i].Cells[0].FindControl("CheckBox1");

            if (cb != null)

            {

                if (cb.Checked)

                {

                    id = GridView1.Rows[i].Cells[1].Text;

                    sc.Add(id);

                }

            }

        }

        DeleteRecords(sc);

        BindGridView();

        totalrecords();

    }

    protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)

    {

        if (e.Row.RowType == DataControlRowType.Header)

        {

            Button b = (Button)e.Row.FindControl("ButtonDelete");

            b.Attributes.Add("onclick", "return ConfirmOnDelete();");

        }

    }

}

Thanks