Pagination not taking value to second page?

$today = date('D, d M, Y');
$sql = "SELECT * FROM table WHERE date = '$today'";
if ($_POST!="") {   
    $mydate = mysql_real_escape_string($_POST['datepicker']);
    if ($mydate != "") {    
        $sql = "SELECT * FROM table WHERE date = '$mydate'";    
    }       
}
$num_results_per_page = 8;
$num_page_links_per_page = 5;
$pg_param = "";
$result=mysql_query($sql);
$row = mysql_fetch_array($result);
pagination($sql, $num_results_per_page, $num_page_links_per_page, $pg_param);
if($pg_error == '')
{
    if(mysql_num_rows($pg_result) > 0)
    {
        while($data = mysql_fetch_assoc($pg_result))
        { 
            echo "";
        }        
        echo "</br>". $pagination_output; 
    }
    else
    {
        echo "No Data.";
    }
}
else
{
    echo $pg_error; 
}

Pagination is working correctly for select $today. Here pagination is not taking value to second page in the case of select $mydate. If second page of $mydate clicks, again going to $today. ie Second click is not posting $mydate to next page. How can I take the value to second page?

pagination.php

$pg_error = '';
$pg_result = '';
$pagination_output = '';
$max_pages = '';
$page_id = '';
$page_numbers_per_page = '';
$pg_user_param = '';
function pagination($sql, $num_results_per_page, $num_page_links_per_page, $pg_param)
{
global $pg_error, $pg_result, $max_pages, $page_id, $page_numbers_per_page, $pg_user_param; 
$user_sql = $sql;
$page_numbers_per_page = $num_page_links_per_page;
$results_per_page = $num_results_per_page;
$pg_user_param = $pg_param; 
$all_results = mysql_query($user_sql);  
if($all_results)
{   
    if(empty($all_results))
    {
        $total_results = 0; 
    }
    else
    {
        $total_results = mysql_num_rows($all_results); 
    }
    $max_pages = ceil($total_results / $results_per_page);              
    if(isset($_GET['page_id']))
    {           
        $page_id = (int) $_GET['page_id'];          

        if($page_id > $max_pages || empty($page_id))
        {
            $page_id = 1;               
        }
    }
    else
    {
        $page_id = 1;           
    }
    $page_id_temp = ($page_id - 1) * $results_per_page;
    $sql_offset = $page_id_temp;
    $user_sql .= " limit $sql_offset, $results_per_page";       
    $pg_result = mysql_query($user_sql);
    Create_Links();     
}
else
{
    $pg_error = 'Error with the sql query you entered: '.mysql_error();
}
}
function Create_Links()
{
global $pagination_output, $max_pages, $page_id, $page_numbers_per_page, $pg_user_param;
$pg_page_name = htmlspecialchars($_SERVER['PHP_SELF'] );

if($max_pages > 1)
{               
    if($page_id > 1)
    {           
        $first_link = '<a href="'.$pg_page_name.'?page_id=1'.$pg_user_param.'">First</a> ';
    }

    if($page_id < $max_pages)
    {           
        $last_link = '<a href="'.$pg_page_name.'?page_id='.$max_pages . $pg_user_param.'">Last</a> ';
    }
    $pre_id = $page_id - 1;
    if($pre_id != 0)
    {
        $pre_link = '<a href="'.$pg_page_name.'?page_id='.$pre_id . $pg_user_param.'">Previous</a> ';
    }       
    $next_id = $page_id + 1;
    if($next_id <= $开发者_开发知识库max_pages)
    {
        $next_link = '<a href="'.$pg_page_name.'?page_id='.$next_id . $pg_user_param.'">Next</a> ';
    }

    if($page_id >= $page_numbers_per_page)
    {

        $start_point = ($page_id - $page_numbers_per_page) + 2;
    }
    else
    {           
        $start_point = 1;
    }

    $loop_num = ($start_point + $page_numbers_per_page) - 1; 
    if($loop_num > $max_pages)
    {
        $loop_num = $max_pages;
    }
    $pagination_output = '<div class="pagination"> ';
    $pagination_output .= $first_link;
    $pagination_output .= $pre_link;        
    for($i = $start_point; $i <= $loop_num; $i++)
    {
        if($i == $page_id)
        {
            $pagination_output .= '<a class="current">'.$i.'</a> ';
        }
        else
        {
            $pagination_output .= '<a href="'.$pg_page_name.'?page_id='.$i . $pg_user_param.'">'.$i.'</a> ';
        }
    }       
    $pagination_output .= $next_link;
    $pagination_output .= $last_link;       
    $pagination_output .= '</div><br />';
}
}
?>

function pagination in your code is not returning the resulting mysql query resource, and your code is not receiving that from the pagination function call

you need to add return $pg_result; in your pagination function

and add $result=pagination(....

Edit: Sorry, I noticed you added pg_result to global, which does not need return and the solution I said, but you don't need mysql_query and fetch before that and I don't see where you print the results. there is only echo "", you can try the one I edited last, and see if it works for you.

Edit:

$today = date('D, d M, Y');
$sql = "SELECT * FROM table WHERE date = '$today'";
if ($_POST!="") {   
    $mydate = mysql_real_escape_string($_POST['datepicker']);
    if ($mydate != "") {    
        $sql = "SELECT * FROM table WHERE date = '$mydate'";    
    }       
}
$num_results_per_page = 8;
$num_page_links_per_page = 5;
$pg_param = "";
//$result=mysql_query($sql);
$pg_result=pagination($sql, $num_results_per_page, $num_page_links_per_page, $pg_param);


if($pg_error == '' && is_resource($pg_result))
{

    if(mysql_num_rows($pg_result) > 0)
    {
        while($data = mysql_fetch_assoc($pg_result))
        { 
            var_dump($data);
        }        
        echo "</br>". $pagination_output; 
    }
    else
    {
        echo "No Data.";
    }
}
else
{
    echo $pg_error; 
}

pagination.php

$pg_error = '';
$pg_result = '';
$pagination_output = '';
$max_pages = '';
$page_id = '';
$page_numbers_per_page = '';
$pg_user_param = '';
function pagination($sql, $num_results_per_page, $num_page_links_per_page, $pg_param)
{
global $pg_error, $pg_result, $max_pages, $page_id, $page_numbers_per_page, $pg_user_param; 
$user_sql = $sql;
$page_numbers_per_page = $num_page_links_per_page;
$results_per_page = $num_results_per_page;
$pg_user_param = $pg_param; 
$all_results = mysql_query($user_sql);  
if($all_results)
{   
    if(empty($all_results))
    {
        $total_results = 0; 
    }
    else
    {
        $total_results = mysql_num_rows($all_results); 
    }
    $max_pages = ceil($total_results / $results_per_page);              
    if(isset($_GET['page_id']))
    {           
        $page_id = (int) $_GET['page_id'];          

        if($page_id > $max_pages || empty($page_id))
        {
            $page_id = 1;               
        }
    }
    else
    {
        $page_id = 1;           
    }
    $page_id_temp = ($page_id - 1) * $results_per_page;
    $sql_offset = $page_id_temp;
    $user_sql .= " limit $sql_offset, $results_per_page";       
    $pg_result = mysql_query($user_sql);
    Create_Links();
            return $pg_result;
}
else
{
    $pg_error = 'Error with the sql query you entered: '.mysql_error();
}

}
function Create_Links()
{
global $pagination_output, $max_pages, $page_id, $page_numbers_per_page, $pg_user_param;
$pg_page_name = htmlspecialchars($_SERVER['PHP_SELF'] );

if($max_pages > 1)
{               
    if($page_id > 1)
    {           
        $first_link = '<a href="'.$pg_page_name.'?page_id=1'.$pg_user_param.'">First</a> ';
    }

    if($page_id < $max_pages)
    {           
        $last_link = '<a href="'.$pg_page_name.'?page_id='.$max_pages . $pg_user_param.'">Last</a> ';
    }
    $pre_id = $page_id - 1;
    if($pre_id != 0)
    {
        $pre_link = '<a href="'.$pg_page_name.'?page_id='.$pre_id . $pg_user_param.'">Previous</a> ';
    }       
    $next_id = $page_id + 1;
    if($next_id <= $max_pages)
    {
        $next_link = '<a href="'.$pg_page_name.'?page_id='.$next_id . $pg_user_param.'">Next</a> ';
    }

    if($page_id >= $page_numbers_per_page)
    {

        $start_point = ($page_id - $page_numbers_per_page) + 2;
    }
    else
    {           
        $start_point = 1;
    }

    $loop_num = ($start_point + $page_numbers_per_page) - 1; 
    if($loop_num > $max_pages)
    {
        $loop_num = $max_pages;
    }
    $pagination_output = '<div class="pagination"> ';
    $pagination_output .= $first_link;
    $pagination_output .= $pre_link;        
    for($i = $start_point; $i <= $loop_num; $i++)
    {
        if($i == $page_id)
        {
            $pagination_output .= '<a class="current">'.$i.'</a> ';
        }
        else
        {
            $pagination_output .= '<a href="'.$pg_page_name.'?page_id='.$i . $pg_user_param.'">'.$i.'</a> ';
        }
    }       
    $pagination_output .= $next_link;
    $pagination_output .= $last_link;       
    $pagination_output .= '</div><br />';
}
}
?>

Looks like you're mixing up the concept of $_POST and $_GET.

By having your pagination links point to '<a href="'.$pg_page_name.'?page_id='.$i . $pg_user_param.'"... You should be intercepting $_GET['page_id'] before you make your SQL query.

Your top code references $_POST['datepicker'] but you don't mention a form anywhere and your pagination links certainly aren't posting that data in your example.

You should use $pg_param = ""; to pass your own query parameters. Ex: &date=$date_value:

$pg_param = "&date=$date_value";