php分页：

<?php     /**    * php padding    */    header("content-type:text/html;charset=utf-8");    //数据库连接    $conn = MySQL_connect("localhost", "root", "111") or die("not connnected : ".mysql_error());    mysql_select_db("test", $conn);    mysql_query("set names utf8");    //查询共有多少行数据    $sql1 = "select count(*) from user";    $ret1 = mysql_query($sql1);    $row1 = mysql_fetch_row($ret1);    $tot = $row1[0];     //每页多少行数据    $length = 5;          //总页数      $totpage = ceil($tot / $length);    //当前页数    $page = @$_GET['p'] ? $_GET['p'] : 1;    //limit 下限    $offset = ($page - 1) * $length;    echo "<center>";    echo "<h2>php padding</h2>";    echo "<table width='700px' border='1px' >";    echo "<tr>";    echo "<th>ID</th>";    echo "<th>USER</th>";    echo "<th>PASS</th>";    echo "</tr>";    //将查询出来的数据用表格显示    $sql2 = "select * from user order by id limit {$offset}, {$length}";    $ret2 = mysql_query($sql2);    while ($row2 = mysql_fetch_assoc($ret2)) {        echo "<tr>";        echo "<td>{$row2['id']}</td><td>{$row2['name']}</td><td>{$row2['pass']}</td>";        echo "</tr>";    }    echo "</table>";    //上一页和下一页    $PRevpage = $page - 1;    if ($page >= $totpage) {        $nextpage = $totpage;    } else {        $nextpage = $page + 1;    }    //跳转    echo "<h3><a href='index.php?p={$prevpage}'>上一页</a>|<a href='index.php?p={$nextpage}'>下一页</a></h3>";    echo "</center>";

核心点：<1>“$sql2 = "select * from user order by id limit {$offset}, {$length}";”，$offset、$length和页数之间的关系。

　　　　<2>上一页和下一页的获得方式，以及临界点。