What event should fire for textbox while searching name in database

select * from student_details where (child_name like @Student_ID or student_id like @Child_Name) and School_Name=@School_Name

protected void txtSearch_TextChanged(object sender, EventArgs e)
       {
           gridviewCandidateDetails.Visible = true;
           SqlCommand cmdSearch = DBManager.DataAccess.command();
           cmdSearch.Parameters.Add(new SqlParameter("@option", SqlDbType.VarChar, 50));
           cmdSearch.Parameters["@option"].Value = "SearchByNameOrRegistrationID";

           cmdSearch.Parameters.Add(new SqlParameter("@School_Name", SqlDbType.NVarChar, 200));
           cmdSearch.Parameters["@School_Name"].Value = Session["SchoolName"].ToString();

           cmdSearch.Parameters.Add(new SqlParameter("@Student_ID", SqlDbType.VarChar, 50));
           cmdSearch.Parameters["@Student_ID"].Value = txtSearch.Text;

           cmdSearch.Parameters.Add(new SqlParameter("@Child_Name", SqlDbType.VarChar, 50));
           cmdSearch.Parameters["@Child_Name"].Value = txtSearch.Text;

           string sqlquery = "SchoolProc";
           DataSet dsPickSearchDetails = DBManager.DataAccess.getdata(sqlquery);
           if (dsPickSearchDetails.Tables[0].Rows.Count > 0)
           {
               gridviewCandidateDetails.DataSource = dsPickSearchDetails.Tables[0];
               gridviewCandidateDetails.DataBind();
               txtSearch.Focus();
           }
           else
           {
               string strScript = "<script>";
               strScript += "alert('Sorry No records Available');";
               strScript += "</script>";
               Page.RegisterClientScriptBlock("strScript", strScript);
               gridviewCandidateDetails.Visible = false;
               txtSearch.Focus();
           }
       }<pre>