PHP paging principle and page jump examples

select * from table limit 0,10 // The first 10 records
select * from table limit 10,10 // The 11th to 20th records
select * from table limit 20,10 // The 21st to 20th records 30 records
...

This set of sql statements is actually the sql statement for fetching each page of data in the table when $pagesize=10. We can summarize such a template: select * from table limit ($currentpageid - 1) * $pagesize, $pagesize Take this template and substitute the corresponding values ​​​​and compare it with the above set of sql statements to see if that is the case. After solving the most important problem of how to obtain the data, all that is left is to pass the parameters, construct the appropriate SQL statement and then use PHP to obtain the data from the database and display it.

php paging code:

// Establish database connection
$link = mysql_connect("localhost", "mysql_user", "mysql_password")
 or die("could not connect: " . mysql_error());
// Get the current page number
if( isset($_get['page']) ){
 $page = intval( $_get['page'] );
}
else{
 $page = 1;
}
// Number of pages per page
$pagesize = 10;
// Get the total amount of data
$sql = "select count(*) as amount from table";
$result = mysql_query($sql);
$row = mysql_fetch_row ($result);
$amount = $row['amount'];
// Calculate how many pages there are in total
if( $amount ){
 if( $amount < $page_size ){ $page_count = 1; } //If the total data amount is less than $pagesize, then there is only one page
 if( $amount % $page_size ){ //The remainder of dividing the total data amount by the number of pages
 $page_count = (int)($amount / $page_size ) + 1; //If there is a remainder, the number of pages is equal to the total data amount divided by the number of pages, rounded up and plus one
 }else{
 $page_count = $amount / $page_size; //If there is no remainder, then The number of pages is equal to the total amount of data divided by the number of pages per page
 }
}
else{
 $page_count = 0;
}

// Page turning link
$page_string = '';
if( $page == 1 ){
 $page_string .= 'First page|Previous page|';
}
else{
 $page_string .= 'Previous page|';
}
if( ($page == $page_count) | | ($page_count == 0) ){
 $page_string .= 'next page|last page';
}
else{
 $page_string .= 'Next page|Last page';
}
// Get data and return the result in two-dimensional array format
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();
}
/ / There is no code to display the results, so that is beyond the scope of the discussion. You can simply use the obtained two-dimensional array to display the results using foreach
?>

oo style code, the database connection in the following code is processed using the pear db class

// 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 ; //Number of each page
 var $currentpageid; //Current page number
 var $nextpageid; //Next page
 var $previouspageid; //Previous page
 var $numpages; //Total number of pages
 var $numitems; //Total number of records
 var $isfirstpage; //Whether it is the first page
 var $islastpage; //Whether it is the last page
 var $sql; //SQL query statement

 function pager($option)
 {
 global $db;
 $this->_setoptions($option);
 // Total number of items
 if ( !isset($this->numitems) )
 {
 $res = $db->query( $this->sql);
 $this->numitems = $res->numrows();
 }
 // Total number of pages
 if ( $this->numitems > 0 )
 {
 if ( $this->numitems < $this->pagesize ){ $this->numpages = 1; }
 if ( $this->numitems % $this->pagesize )
 {
 $this- >numpages= (int)($this->numitems / $this->pagesize) + 1;
 }
 else
 {
 $this->numpages = $this->numitems / $this-> ;pagesize;
 }
 }
 else
 {
 $this->numpages = 0;
 }

 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:
 $this->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;
 }

 /***
 *
 * Returns 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, which has less overhead
 * If the result set is not very large, you can Directly use getpagedata to obtain the result in two-dimensional array format
 * The getpagedata method also calls this method to obtain the result
 *
 ***/

 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); //Use pear db::limitquery method to ensure Database compatibility

 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) )
 {
 $this->$key = $value;
 }
 }

 return true;
 }
}
?>

Pagination code call:

// 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
{
 $turnover = "Homepage|previouspageid."&numitems=" .$pager->numitems."'>Previous page|";
}
if ( $pager->islastpage )
{
 $turnover .= "Next page | Last page" ;
}
else
{
 $turnover .= "nextpageid."&numitems=".$pager->numitems."'>next Page|numpages."&numitems=".$pager->numitems."'>Last Page" ;
}
?>

Instructions: This class only processes data and is not responsible for display, because it is a bit reluctant to put both data processing and result display into one class. The situation and requirements during display are changeable. It is better to process 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, to display the user pagination list:

class memberpager extends pager
{
 function showmemberlist()
 {
 global $db;

 $data = $this->getpagedata();
// Code to display the results
 // ......
 }
}
/// Call
if ( isset($_get['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();
?>

Second, the compatibility of different databases in different databases The way to write a section of intercepted results is different.

$pagenum=@ceil($num/$pagesize);
if($num > $pagesize){
 if($ pageval<=1) $pageval=1;
 if($pageval==$pagenum){
 echo "Homepage Previous page Next page < a href='$url?page=".$pagenum."'>Last page";
 //echo "page".$pageval."/total".$pagenum."page" ;
 echo " to n"; 
 for ($i = 1 ; $i <= $pagenum; $i++) {  if ($i == $pageval)  echo "$in"; 
 else 
 echo "$in"; 
 } 
 echo " pages of $pagenum pages";
}
 }
}
 ?>

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