When you scroll down a page with a long table on it, typically the header of the table scrolls away and becomes useless. This code clones the table header and applies it at the top of the page once you have scrolled beyond it, and disappears when you have scrolled past the table.

View Demo

function UpdateTableHeaders() {
   $("div.divTableWithFloatingHeader").each(function() {
       offset = $(this).offset();
       scrollTop = $(window).scrollTop();
       if ((scrollTop > offset.top) && (scrollTop < offset.top + $(this).height())) {
           $(".tableFloatingHeader", this).css("visibility", "visible");
           $(".tableFloatingHeader", this).css("top", Math.min(scrollTop - offset.top, $(this).height() - $(".tableFloatingHeader", this).height()) + "px");
       }
       else {
           $(".tableFloatingHeader", this).css("visibility", "hidden");
           $(".tableFloatingHeader", this).css("top", "0px");
       }
   })
}

$(document).ready(function() {
   $("table.tableWithFloatingHeader").each(function() {
       $(this).wrap("<div class="divTableWithFloatingHeader" style="position:relative"></div>");
       $("tr:first", this).before($("tr:first", this).clone());
       clonedHeaderRow = $("tr:first", this)
       clonedHeaderRow.addClass("tableFloatingHeader");
       clonedHeaderRow.css("position", "absolute");
       clonedHeaderRow.css("top", "0px");
       clonedHeaderRow.css("left", "0px");
       clonedHeaderRow.css("visibility", "hidden");
   });
   UpdateTableHeaders();
   $(window).scroll(UpdateTableHeaders);
});

Reference URL