页面首页、上一页、下一页、尾页设置

<?php
$page = empty ($_GET['page']) ? 1: $_GET['page'] ;
include "connect.php";
// $conn = mysqli_connect('localhost','root','');
// if(!$conn)
// {
//     exit('数据库连接失败');
// }

mysqli_set_charset($conn ,'utf8');
mysqli_select_db($conn ,'test');
//----------------------------------------分页开始---
// $page = 1;
//求出来总条数
$sql = "select count(*) as count from liuyan";  //获取当前数据表中有多少条数据 可能
$result = mysqli_query($conn,$sql);
$pageRes = mysqli_fetch_assoc($result);
$count = $pageRes['count'];
//每页显示数, 假设每页显示5条数据
$num = 5;
//根据每页显示数可以求出总页数
$pageCount = ceil($count/$num);
//根据总页数求出偏移量
$offset = ($page-1) * $num;
//----------------------------------------分页结束---


 $sql = "select * from liuyan limit " .$offset . ',' . $num ; //注意limit 要和"之间有空格！！！！！！！！！！要不然出错
// $sql = "select * from liuyan";

$obj = mysqli_query($conn, $sql);
echo '<a href="add.php">添加</a>';
echo '<table width = "600" border="1">';
    echo '<th>id</th><th>username</th><th>address</th><th>sex</th><th>age</th><th>date</th><th>option</th>';    //类型
        while($rows = mysqli_fetch_assoc($obj))
        {
        echo '<tr>';
            echo '<td>'.$rows['id'].'</td>';
            echo '<td>'.$rows['username'].'</td>';
            echo '<td>'.$rows['address'].'</td>';
            echo '<td>'.$rows['sex'].'</td>';
            echo '<td>'.$rows['age'].'</td>';
            echo '<td>'.$rows['date'].'</td>';
            echo '<td><a href="del.php?id='.$rows['id'].'" >删除</a>/<a href="update.php?id='.$rows['id'].'">修改</a></td>';//id='.$rows['id'].'  获取到操作组的id
         echo '</tr>';   
        }
echo '</table>';
//
$next = $page + 1;
$prev = $page - 1;
if($prev < 1)
{
    $prev = 1; 
}
if($next > $pageCount)
{
    $next = $pageCount;
}
mysqli_close($conn);
?>
<!-- 对按钮进行 -->
<a href="index.php?page=1">首页</a>&nbsp;&nbsp;&nbsp;
<a href="index.php?page=<?=  $prev;?>">上一页</a>&nbsp;&nbsp;&nbsp;
<a href="index.php?page=<?= $next; ?>">下一页</a>&nbsp;&nbsp;&nbsp;
<a href="index.php?page=<?= $pageCount; ?>">尾页</a>