PHP에서 페이징을 구현하는 원리와 단계

<?php
//数据库服务器
define(&#39;DB_HOST&#39;, &#39;localhost&#39;);
//数据库用户名
define(&#39;DB_USER&#39;, &#39;root&#39;);
//数据库密码
define(&#39;DB_PWD&#39;, &#39;secret&#39;);
//库名
define(&#39;DB_NAME&#39;, &#39;book&#39;);
//字符集
define(&#39;DB_CHARSET&#39;, &#39;utf8&#39;);

<?php
include &#39;config.php&#39;;$conn = mysqli_connect(DB_HOST, DB_USER, DB_PWD, DB_NAME);
if (mysqli_errno($conn))
 {  mysqli_error($conn);
    exit;
  }
mysqli_set_charset($conn, DB_CHARSET);
?>

include 'connection.php';

limit offset , num

offset的值为 (n-1)*5
num 为规定的5

通过查询user表的count(id),得到总数$count。
$count_sql = 'select count(id) as c from user';
$result = mysqli_query($conn, $count_sql);
$data = mysqli_fetch_assoc($result);
//得到总的用户数
$count = $data['c'];

$page = isset($_GET['page']) ? (int) $_GET['page'] : 1;

if (isset($_GET['page'])) {
    $page = (int) $_GET['page'];
} else {
    $page = 1;
}

//每页显示数
$num = 5;
$total = ceil($count / $num);

if ($page <= 1) {
    $page = 1;
}
if ($page >= $total) {
    $page = $total;
}

$num = 5;
$offset = ($page - 1) * $num;

$sql = "select id,username,createtime,createip from user order by id desc limit $offset , $num";

echo &#39;<tr>
    <td colspan="5">
    <a href="page.php?page=1">首页</a>
    <a href="page.php?page=&#39; . ($page - 1) . &#39;">上一页</a>
    <a href="page.php?page=&#39; . ($page + 1) . &#39;">下一页</a>
    <a href="page.php?page=&#39; . $total . &#39;">尾页</a>
    当前是第 &#39; . $page . &#39;页  共&#39; . $total . &#39;页
    </td>
    </tr>&#39;;