Pagination keeps showing the same portion of SQL data

Question

I have a really large data set from SQL that i need to paginate.

I have an issue with my pagination code. The code does show the page number in the URL

Answer 1

You should change

$sql='SELECT * FROM ETF';
$result = mysqli_query($con, $sql);
$number_of_results = mysqli_num_rows($result);

to something like this

$count = mysqli_fetch_assoc(mysqli_query($con,"SELECT COUNT(*) AS RC FROM ETF"));
$number_of_results=$count['RC'];

because it is faster to get count from mysql (index if its a large table) instead of fetching all table data (because SELECT *...) for looping trough it just for row counting.

// retrieve selected results from database and display them on page
$sql='SELECT * FROM ETF LIMIT ' . $this_page_first_result . "," .$results_per_page;

You using good query, but using wrong function to get its results.

Query should be

$sql='SELECT * FROM ETF LIMIT ' . $results_per_page . "," .$this_page_first_result;

or:

$sql='SELECT * FROM ETF LIMIT ' . $results_per_page . " OFFSET " .$this_page_first_result;

Both of these work.

Change

while($row = mysqli_fetch_array($result)) {
  echo $row['ETF'] . ' ' . $row['ETF NAME']. '<br>';
}

to

while($row = mysqli_fetch_assoc($result)) {
  echo $row['ETF'] . ' ' . $row['ETF NAME']. '<br>';
}

because "mysqli_fetch_array" fetch array width numbered indexes (for example 0, 1, 2...) not a text ones you are trying to use, but "mysqli_fetch_assoc" does that you need.

Full code should be

<?php
$con=mysqli_connect('your server','login to database','database logins password','database name');
// define how many results you want per page
$results_per_page=10;
// find out the number of results stored in database
$count=mysqli_fetch_assoc(mysqli_query($con,"SELECT COUNT(*) AS RC FROM ETF"));
$number_of_results=$count['RC'];
// determine number of total pages available
$number_of_pages=ceil($number_of_results/$results_per_page);
// determine which page number visitor is currently on
if(!isset($_GET['page']))
{
    $page=1;
}
else
{
    $page=$_GET['page'];
}
// determine the sql LIMIT starting number (OFFSET) for the results on the displaying page
$this_page_first_result=($page-1)*$results_per_page;
// retrieve selected results from database and display them on page
$sql="SELECT * FROM ETF LIMIT $results_per_page,$this_page_first_result";
$result=mysqli_query($con, $sql);
// Loop to show results
while($row = mysqli_fetch_assoc($result))
{
    echo $row['ETF'].' '.$row['ETF NAME'].'<br>';
}
// display the links to the pages
for($page=1;$page<=$number_of_pages;$page++)
{
    echo'<a href="?page='.$page.'">'.$page.'</a> ';
}
mysqli_close($con);
    ?>

Answer 2

Try:

$sql='SELECT * FROM ETF LIMIT ' . $results_per_page . ' OFFSET ' . $this_page_first_result;

Also as mentioned you should sort by a certain column with 'ORDER BY' for consistent results.

Answer 3

Using OFFSET and LIMIT for pagination of web pages leads to two bugs -- duplicated rows shown, and rows not shown.

Why?

1. You are pondering the "first" 10 rows on one web page.
2. Meanwhile a row is INSERTed or DELETEd that belongs in the first 10.
3. You click [Next] and go to the page that shows the next 10 rows. But wait, it is not showing the "next" 10 rows, it is showing rows #11-20. And, since something changed in rows 1-10, the rows are not really continuing where you left off.

I just gave you a hint of how to avoid it -- "remember where you left off" instead of using OFFSET. More .