PHP paging algorithm - Dynamic web programming

Condition before reading the article:

• You must know how to connect to the DB.

• You have created a table and the table contains informations to wait ... paging

You create a file list.php has a complete code as follows:

<?php  $page = isset ( $_GET["page"] ) ? intval ( $_GET["page"] ) : 1; 
$rows_per_page = 20; 
$page_start = ( $page - 1 ) * $rows_per_page; 
$page_end = $page * $rows_per_page; 
$sql_query = mysql_query("SELECT * FROM table_name"); 
$number_of_page = ceil ( mysql_num_rows( $sql_query ) / $rows_per_page ); 
if ( $number_of_page > 1 ) 
{ 
$list_page = " <td> Page: </td>"; 
for ( $i = 1; $i <= $number_of_page; $i++ ) 
{ 
if ( $i == $page ) 
{ 
$list_page .= " <td>[ <b>{$i}</b> ]</td> "; 
} 
else 
{ 
$list_page .= "<td><a href=’list.php?page={$i}’> {$i} </a></td>"; 
} 
} 
} 
$i = 0; 
while ( $result = mysql_fetch_array ( $sql_query ) ) 
{ 
if ( $i >= $page_start ) 
{ 
print ""; 
} 
$i++; 
if ($i >= $page_end) 
{ 
break; 
}
} 
print <<<EOF 
<table cellspacing="0" cellpadding="0" border="0"> 
<tr> 
{$list_page} 
</tr> 
</table> 
EOF;
?> 

Explain each paragraph:

• The syntax of this passage is:
Page = check variable page exists or not [?]
If exists, get the value of this variable and use the function filter intval to receive safe values [:]
If not then will have the default value is 1:

 $page=isset($_GET["page"])?intval($_GET["page"]):1;

• Numbers of line on a page:

$rows_per_page = 20;

• Count the number of lines in the opening page based on variable $page:

$page_start=($page-1)*$rows_per_page;

• Count the number of lines in the last page based on variable $page:

$page_end=$page*$rows_per_page;

Example of the opening page and last page according to the above formula:

Suppose the page being viewed is 1, we are 

$page_start=(1-1)*20=0

And 

$page_start = (1 - 1) * 20 = 0 

So we have a value 0 is begin and 20 is end.

• Retrieve into table_name: 

$sql_query = mysql_query("SELECT * FROM table_name");

• Count the numbers of page, do by following:

mysql_num_rows($sql_query);

is the table's total number of lines have retrieved [1]

$rows_per_page

is equal to 20 ( above value that we have set) [2]
Getting [1] divided by [2] It will be several pages
To rounding values ​​from (x.1 -> x.9 of 1 + x) we use the function ceil ()

$number_of_page=ceil( mysql_num_rows( $sql_query )/$rows_per_page); 

• If the page number is greater than 1 then it will list the pages

if ( $number_of_page > 1 ) 
{ 
$list_page = "<td> Page: </td>";  
for ( $i = 1; $i <= $number_of_page; $i++ ) 
{ 
if ( $i == $page ) 
{ 
$list_page .= "<td> [ <b> {$i} </b>] </td>"; 
} 
else 
{ 
$list_page .= "<td><a href=’list.php?page={$i}’> {$i} </a></td>";  
} 
} 
}  

• Set variable $i equal zero.
$i = 0;
• List all lines in a table.

while ( $result = mysql_fetch_array ( $sql_query ) ) 
{if ( $i >= $page_start ) 
{ 
print $result[content];  
} $i++; 
if ($i >= $page_end) 
{ 
break; 
} 
}

• Above we loaded content to variable $list _ page, now we print it.

print <<<EOF 
<table cellspacing="0" cellpadding="0" border="0"> 
<tr> 
{$list_page} 
</tr> 
</table> 
EOF

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