php下的分页原理学习

**首先确定分页需要确定的参数数据**
`page 当前页码`
`pageSize 每一页的条数`
`total_count 总共的数据条数`
`pageNumber = ceil ( totalCount / pageSize) 总共可以分为几页`

begin :
**1.首先需要正确的连接数据库查询下总条数信息**

//配置数据库信息
$host = "localhost:3306";
$username = "root";
$password = "";//密码
$db = "";//表名

//创建数据库链接
$conn = mysqli_connect($host, $username, $password, $db);
if (!$conn) {
echo "connect error";
exit;
}

if ($result = mysqli_query($conn, "SELECT COUNT(*) FROM 表名")) {
$row = mysqli_fetch_assoc($result);
$total_count = $row['COUNT(*)'];//获得总共的数据条数
}

　　

php5.5 以后废弃了之前的mysql_XXX的 api 操作 改用 mysqli_XXX的 api;

**2.判断边界条件生成sql语句**
`sql`语句：`"SELECT * FROM 表名 LIMIT 起始位置,数量"`

//获得www.domain.com/xxx/xxx?page=num;url的参数
$page = $_GET['page'];

//总共可分的页数
$pageNumber = ceil($total_count / $pageSize);

if ($page <= 0 || $page > $pageNumber ) {
echo '404';//非法的page参数直接返回404
exit;
} else {
$start = ($page - 1) * 10;
}

if($result = mysqli_query($conn, "SELECT * FROM 表名 LIMIT $start,10")){ 
while ($row = mysqli_fetch_assoc($result)) {
echo $row['id'], ' ', $row['name'], "<br/>"; //查询出结果
}
}

　　

**3.前端分页的显示和url**

//边界条件判定来确定 `上一页` `下一页` 按钮的显示和是否可以点击； -1表示无效，即不可点击
if ($page <= 1) {
$pre = -1;
} else {
$pre = $page - 1;
}

if ($page < $pageNumber) {
$next = $page + 1;
} else {
$next = -1;
}

$path = $_SERVER["PHP_SELF"];
if ($pre == -1) {
echo "<span class='pagination'>上一页</span>";
} else {
echo "<a class='pagination' href='$path?page=$pre'>上一页</a>";
}
if ($page == 1) {
echo "<span class='pagination'>首页</span>";
} else {
echo "<a class='pagination' href='$path?page=1'>首页</a>";
}
//分页页码按钮的显示逻辑
// $paginationSize= 5;
//默认显示5个连续的可点击分页页码按钮
//页码数量超过一定数值后显示前两页
if (($page + $paginationSize) > $next_limit) {
$end_page = $next_limit;
} else {
$end_page = $page + $paginationSize;
}
if ($page > 4) {
echo "<a class='pagination' href='$path?page=1'>1</a>";
echo "<a class='pagination' href='$path?page=2'>2</a>";
echo "<span class='point'>···</span>";
}
for ($i = $end_page - $paginationSize; $i <= $end_page; $i++) {
if ($i == $page) {
echo "<span class='pagination'>$i</span>";
} else {
echo "<a class='pagination' href='$path?page=$i'>$i</a>";
}
}
if ($page == $next_limit) {
echo "<span class='pagination'>尾页</span>";
} else {
echo "<a class='pagination' href='$path?page=$next_limit'>尾页</a>";
}
if ($next == -1) {
echo "<span class='pagination' >下一页</span>";
} else {
echo "<a class='pagination' href='$path?page=$next'>下一页</a>";
}

　　

end:

完整代码：
[github][1]

[1]: https://github.com/llauser/hand-demo/tree/master/php