PHP dynamic previous/next links - php

Question

I have a table called "product".
I'm displaying all the data from PHP product view page by using the id parameter.
With my code:
if(isset($_GET['id'])) {
$id = $_GET['id'];
}
$query = "SELECT * FROM product WHERE id = $id ";
$select_product = $db->query($query);
while($row = $db->fetch_object($select_product)) {
$status = $row->status;
if($status == 'published') {
$title = $row->title;
echo $title;
}
}
I can pull all the data I need. In this example I can echo the title.
But how do I display a dynamic next page link? That goes same for previous link.
When I try with this code:
$query = "SELECT id FROM product";
$select_ids = $db->query($query);
while($row = $db->fetch_object($select_ids)) {
$ids = $row->id;
echo $ids;
}
I can see all the pages from that table. In my case they are 20,21,22...28
Next, I've tried like this:
$query = "SELECT id from product";
$select_ids = $db->query($query);
if($select_ids->num_rows > 0) {
$next = $id + 1;
echo 'Next';
} else {
}
With this code, my "next" link successfully goes to the next page. But, when it finishes with the result, in this case when I'm on page 28, the next dynamic link goes to empty page (29). Also this is not a good approach, because if some page, let's say 25 is deleted, the next link won't skip that page.
How can I improve that dynamic "next" link?

Answer 1

So first of all, you need two queries one for getting the data to display and another for counting the number of rows, also we'll need some additional variables.
Here comes the code:
$page = 1;
if(isset($_GET['page'])) {
$page = $_GET['page'];
}
$numberOfResultsPerPage = 10;
$offset = $numberOfResultsPerPage * ($page - 1)
$count = $db->query("SELECT COUNT(id) as num FROM product");
while($row = $db->fetch_object($count)) {
$numberOfRows = $row->num;
}
$query = "SELECT id FROM product LIMIT ". $offset.", ".$numberOfResultsPerPage;
$select_ids = $db->query($query);
while($row = $db->fetch_object($select_ids)) {
$ids = $row->id;
echo $ids;
}
if($page > 1) {
echo 'Prev';
}
if($page < ceil($numberOfRows / $numberOfResultsPerPage)) {
echo 'Next';
}
UPDATE:
In case you need to just find the next and previous product of the product this is the solution. It is not good if you'll have lots of products but in case the number of products is under 1000 there should not be any problems:
if(isset($_GET['id'])) {
$id = $_GET['id'];
}
$query = "SELECT id from product";
$select_ids = $db->query($query);
$ids = array();
$i = 0;
while($row = $db->fetch_object($select_ids)) {
$ids[$i] = $row->id;
if($row->id == $id) {
$index = $i;
}
$i++;
}
if(isset($ids[$index-1])) {
echo 'Prev';
}
if(isset($ids[$index+1])) {
echo 'Next';
}