1、前言

分頁顯示是一種非常常見的瀏覽和顯示大量數(shù)據(jù)的方法，屬于web編程中最常處理的事件之一。對(duì)于web編程的老手來說，編寫這種代碼實(shí)在是和呼吸一樣自然，但是對(duì)于初學(xué)者來說，常常對(duì)這個(gè)問題摸不著頭緒，因此特地撰寫此文對(duì)這個(gè)問題進(jìn)行詳細(xì)的講解，力求讓看完這篇文章的朋友在看完以后對(duì)于分頁顯示的原理和實(shí)現(xiàn)方法有所了解。本文適合初學(xué)者閱讀，所有示例代碼均使用php編寫。

2、原理

所謂分頁顯示，也就是將數(shù)據(jù)庫中的結(jié)果集人為的分成一段一段的來顯示，這里需要兩個(gè)初始的參數(shù)：

每頁多少條記錄（$PageSize）？
當(dāng)前是第幾頁（$CurrentPageID）？

現(xiàn)在只要再給我一個(gè)結(jié)果集，我就可以顯示某段特定的結(jié)果出來。
至于其他的參數(shù)，比如：上一頁（$PreviousPageID）、下一頁（$NextPageID）、總頁數(shù)（$numPages）等等，都可以根據(jù)前邊這幾個(gè)東西得到。
以mysql數(shù)據(jù)庫為例，如果要從表內(nèi)截取某段內(nèi)容，sql語句可以用：select * from table limit offset, rows?？纯聪旅嬉唤Msql語句，嘗試一下發(fā)現(xiàn)其中的規(guī)率。

前10條記錄：select * from table limit 0,10
第11至20條記錄：select * from table limit 10,10
第21至30條記錄：select * from table limit 20,10
……

這一組sql語句其實(shí)就是當(dāng)$PageSize=10的時(shí)候取表內(nèi)每一頁數(shù)據(jù)的sql語句，我們可以總結(jié)出這樣一個(gè)模板：

select * from table limit ($CurrentPageID - 1) * $PageSize, $PageSize

拿這個(gè)模板代入對(duì)應(yīng)的值和上邊那一組sql語句對(duì)照一下看看是不是那么回事。搞定了最重要的如何獲取數(shù)據(jù)的問題以后，剩下的就僅僅是傳遞參數(shù)，構(gòu)造合適的sql語句然后使用php從數(shù)據(jù)庫內(nèi)獲取數(shù)據(jù)并顯示了。以下我將用具體代碼加以說明。

3、簡單代碼
請?jiān)敿?xì)閱讀以下代碼，自己調(diào)試運(yùn)行一次，最好把它修改一次，加上自己的功能，比如搜索等等。

// 建立數(shù)據(jù)庫連接
$link = mysql_connect("localhost", "mysql_user", "mysql_password")
or die("Could not connect: " . mysql_error());
// 獲取當(dāng)前頁數(shù)
if( isset($_GET['page']) ){
$page = intval( $_GET['page'] );
}
else{
$page = 1;
}
// 每頁數(shù)量
$PageSize = 10;
// 獲取總數(shù)據(jù)量
$sql = "select count(*) as amount from table";
$result = mysql_query($sql);
$row = mysql_fetch_row($result);
$amount = $row['amount'];
// 記算總共有多少頁
if( $amount ){
if( $amount < $page_size ){ $page_count = 1; } //如果總數(shù)據(jù)量小于$PageSize，那么只有一頁
if( $amount % $page_size ){ //取總數(shù)據(jù)量除以每頁數(shù)的余數(shù)
$page_count = (int)($amount / $page_size) + 1; //如果有余數(shù)，則頁數(shù)等于總數(shù)據(jù)量除以每頁數(shù)的結(jié)果取整再加一
}else{
$page_count = $amount / $page_size; //如果沒有余數(shù)，則頁數(shù)等于總數(shù)據(jù)量除以每頁數(shù)的結(jié)果
}
}
else{
$page_count = 0;
}

// 翻頁鏈接
$page_string = '';
if( $page == 1 ){
$page_string .= '第一頁|上一頁|';
}
else{
$page_string .= '第一頁|上一頁|';
}
if( ($page == $page_count) || ($page_count == 0) ){
?? $page_string .= '下一頁|尾頁';
}
else{
?? $page_string .= '下一頁|尾頁';
}
// 獲取數(shù)據(jù)，以二維數(shù)組格式返回結(jié)果
if( $amount ){
?? $sql = "select * from table order by id desc limit ". ($page-1)*$page_size .", $page_size";
?? $result = mysql_query($sql);

?? while ( $row = mysql_fetch_row($result) ){
?????? $rowset[] = $row;
?? }
}else{
?? $rowset = array();
}
// 沒有包含顯示結(jié)果的代碼，那不在討論范圍，只要用foreach就可以很簡單的用得到的二維數(shù)組來顯示結(jié)果
?>

4、OO風(fēng)格代碼
以下代碼中的數(shù)據(jù)庫連接是使用的pear db類進(jìn)行處理

// FileName: Pager.class.php
// Paging class, this class is only used to process data structures and is not responsible for processing display work
Class Pager
{
var $PageSize; //The number of each page
var $CurrentPageID; Pages
var $numPages; //Total number of pages
var $numItems; //Total number of records
var $isFirstPage; one Page
var $sql;
??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????>?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????> If ( $this->numItems < $this->PageSize ){ $this->numPages = 1; }
If ( $this->numItems % $this->PageSize )
??????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????this->numPages = $this->numItems / $this->PageSize;
}
}
else
?? > }

switch ( $this->CurrentPageID )
{
case $this->numPages == 1:
$this->isFirstPage = true;
$this->isLastPage = true;
break;
case 1:
$this->isFirstPage = true;
$this->isLastPage = false;
break;
case $this->numPages:
$this->isFirstPage = false;
$this->isLastPage = true;
break;
???????????? default:
?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? through >isFirstPage = false;
$this->isLastPage = false;
}

?????? if ( $this->numPages > 1 )
?????? {
?????????? if ( !$this->isLastPage ) { $this->NextPageID = $this->CurrentPageID + 1; }
?????????? if ( !$this->isFirstPage ) { $this->PreviousPageID = $this->CurrentPageID - 1; }
?????? }

?????? return true;
?? }

?? /***
*
* Return the database connection of the result set
* When the result set is relatively large, you can directly use this method to obtain the database connection, and then traverse outside the class, so the overhead is smaller
* If the result set is not very large, you can directly use getPageData to obtain the results in two-dimensional array format
* The getPageData method is also called to obtain the results
*
***/

?? function getDataLink()
?? {
?????? if ( $this->numItems )
?????? {
?????????? global $db;

?????????? $PageID = $this->CurrentPageID;

?????????? $from = ($PageID - 1)*$this->PageSize;
?????????? $count = $this->PageSize;
?????????? $link = $db->limitQuery($this->sql, $from, $count);?? //使用Pear DB::limitQuery方法保證數(shù)據(jù)庫兼容性

?????????? return $link;
?????? }
?????? else
?????? {
?????????? return false;
?????? }
?? }

?? /***
*
* Return the result set in the format of a two-dimensional array
*
***/

?? function getPageData()
?? {
?????? if ( $this->numItems )
?????? {
?????????? if ( $res = $this->getDataLink() )
?????????? {??????
?????????????? if ( $res->numRows() )
?????????????? {
?????????????????? while ( $row = $res->fetchRow() )
?????????????????? {
?????????????????????? $result[] = $row;
?????????????????? }
?????????????? }
?????????????? else
?????????????? {
?????????????????? $result = array();
?????????????? }

?????????????? return $result;
?????????? }
?????????? else
?????????? {
?????????????? return false;
?????????? }
?????? }
?????? else
?????? {
?????????? return false;
?????? }
?? }

function _setOptions($option)
{
$allow_options = array(
'PageSize',
'CurrentPageID',
???????????? 'sql',
????????????? 'numItems '
);

foreach ( $option as $key => $value )
{
if ( in_array($key, $allow_options) && ($value != null) } ??>?>
// FileName: test_pager.php
// This is a simple sample code. The code for using the pear db class to establish a database connection is omitted.
require "Pager.class .php";
if ( isset($_GET['page']) )
{
$page = (int)$_GET['page'];
}
else
{
$page = 1;
}
$sql = "select * from table order by id";
$pager_option = array(
"sql" => $sql ,
"PageSize" => 10,
"CurrentPageID" => $page
);
if ( isset($_GET['numItems']) )
{
$pager_option['numItems'] = (int)$_GET['numItems'];
}
$pager = @new Pager($pager_option);
$data = $pager->getPageData ();
if ( $pager->isFirstPage )
{
$turnover = "Homepage|Previous page|";
}
else
{
$ turnover = "Homepage|Previous Page|";
}
if ( $pager->isLastPage )
{
$turnover .= "Next page|Last page";
}
else
{
$turnover .= "Next Page|Last page";
}
?>


There are two things that need to be explained:

This class only processes data and is not responsible for display, because I think it is a bit reluctant to put both data processing and result display into one class. When displaying, the situation and requirements are changeable. It is better to handle it according to the results given by the class. A better way is to inherit a subclass of your own based on the Pager class to display different paginations. For example, displaying the user pagination list can be:

Class MemberPager extends Pager
{
function showMemberList()

global $db;

$data = $this-> getPageData();

???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????. page']) )
{
$page = (int)$_GET['page'];
}
else
{
$page = 1;
}
$sql = "select * from members order by id";
$pager_option = array(
"sql" => $sql,
"PageSize" => 10,
"CurrentPageID" => $page
);
if ( isset($_GET['numItems']) )
{
$pager_option['numItems'] = (int)$_GET[ 'numItems'];
}
$pager = @new MemberPager($pager_option);
$pager->showMemberList();
?>


The second thing that needs to be explained is the compatibility of different databases. The way to intercept a result in different databases is different.
mysql: select * from table limit offset, rows
pgsql: select * from table limit m offset n
......
So you need to use pear when you want to get the result in the class The limitQuery method of the db class.

Ok, I’ll take credit when I’m done. I hope you don’t feel like it’s a waste of time if you take the time to read these words.