使用php和mysql排序表

I am trying to sort the results from mysql table on the webpage table. I have created buttons(ascending and descending) on required columns. It is working fine for the initial group of data. But when I change to other group of data(say different month) it is redirecting to the initial results page and not to the changed month. I have created this using PHP. One of the table headers is:

print "  <th>";
    print " Clientprint";
    print "  <form action=\"#\" method=\"POST\"><button type=\"submit\" name=\"client_val\" value=\"ASC\" style=\"border:0; background:transparent\" /><img src=\"up-icon.png\" width=\"16\" height=\"16\"></button>";
    print "  <button type=\"submit\" name=\"client_val\" value=\"DESC\" style=\"border:0; background:transparent\" /><img src=\"down-icon.png\" width=\"16\" height=\"16\"></button></form>";
    print " </th>
";