PHP paging code examples have comments

 header("content-type:text/html;charset=utf-8");
 //Database connection
 $conn = mysql_connect("localhost", "root", "111 ") or die("not connnected : ".mysql_error());
 mysql_select_db("test", $conn);
 mysql_query("set names utf8");
 //Query how many rows of data there are in total
 $sql1 = " select count(*) from user";
 $ret1 = mysql_query($sql1);
 $row1 = mysql_fetch_row($ret1);
 $tot = $row1[0];
 //How many rows of data per page
 $length = 5;
 //Total number of pages
 $totpage = ceil($tot / $length);
 //Current number of pages
 $page = @$_GET['p'] ? $_GET['p'] : 1 ;
 //limit lower limit
 $offset = ($page - 1) * $length;
 echo "";
 echo "php padding";
 echo ""; echo ""; echo ""; echo "" ; echo ""; echo ""; //Display the queried data in a table $sql2 = "select * from user order by id limit { $offset}, {$length}"; $ret2 = mysql_query($sql2); while ($row2 = mysql_fetch_assoc($ret2)) { echo ""; echo "" ; echo ""; } echo "

ID
USER
PASS






{ $row2['id']}{$row2['name']}{$row2['pass']}


";
 //Previous page and next page
 $prevpage = $page - 1;
 if ($page >= $totpage) {
 $nextpage = $totpage;
 } else {
 $nextpage = $page + 1;
 }
 //Jump
 echo "Previous page|Next page";
 echo "";

Key points of pagination code: "$sql2 = "select * from user order by id limit {$offset}, {$length}";", the relationship between $offset, $length and the number of pages. How to get the previous page and next page, and the critical point.