PHP howto - Database paging (pagination)

OK, so it’s not quite the nuclear bomb I promised, but it’s just as much fun

Database paging, for those of you who are interested, is when you split the number of results returned by a query into smaller chunks, and then show those one page at a time.  Think of how Google will display 10 results out of 4 236 735.  Same thing.

The basic idea is to:

1. Run your query, limited to the number of desired results
2. Get the number of results that there would have been, without the limit
3. Display the first set of results
4. Build and display <prev> and <next> links, which, when clicked…
5. Display the prev/next set of results, moved down/up by the desired amount
6. Repeat 4 & 5

The following code sample is a very basic implementation of this idea.  I have not checked the code, so apologies in advance if there are any bugs.

<?php
 
$no_results = TRUE;   // No results found yet
$howmany    = 10;     // Return 10 results per query
 
// Set default starting point of query to 0, or, if set, to $_GET['rs']
$row_start  = (isset($_GET['rs'])) ? $_GET['rs'] : 0;
 
 
// Do our SQL query, with something like LIMIT 0, 10
$sql    = "SELECT SQL_CALC_FOUND_ROWS id, name, surname FROM person LIMIT ". $row_start .", ". $howmany ."";
$result = mysql_query($sql);
 
 
// Get the number of rows that would have been returned WITHOUT a limit clause, to be used later for paging.
$count_sql        = "SELECT FOUND_ROWS() AS total";
$count_sql_result = mysql_query($count_sql);
$count_row 	  = mysql_fetch_array($count_sql_result);
$count_result 	  = $count_row['total'];
 
// Start looping through our result set
while($row = mysql_fetch_array($result)) {
    $no_results = FALSE;
 
    // Save results of query to $line_output
    $line_output .= "
        <div class=\"someclassname\">
            <div>". $row['id'] ."</div>
            <div>". $row['name'] ."</div>
            <div>". $row['surname'] ."</div>
        </div>";
}
 
// Don't bother building paging if we don't have records
if ($no_results) {
    $line_output = "No records found...";
    $page_output = "";
}
else {
    // Build <prev> and <next> links and save to $page_output
    $rs_prev = $row_start - $howmany; // where would prev page start, given current start less no. of records
    $rs_next = $row_start + $howmany; // where would next page start, given current start plus no. of records
 
    // If for some reason the next <prev> starting point is negative, do not display <prev>
    // This happens when our current starting point is already 0
    // This may happen if some smartass manually changes the rs= bit in the url
    $page_output_prev 	= ($rs_prev < 0) ? "" : "<a href='?rs=".$rs_prev."'>Previous</a>";
 
    // Will the next page jump start point exceed the number of records returned?
    // If so, don't display <next>'
    $page_output_next 	= ($rs_next >= $count_result) ? "" : "<a href='?rs=".$rs_next."'>Next</a>";
 
    // Just something to put between <prev> & <next>, IF they are both active
    if (($page_output_prev == "") || ($page_output_next == "")) {$page_output_breaker = "";}
    else { $page_output_breaker = " || ";}
 
    // Build final paging output
    $page_output = $page_output_prev . $page_output_breaker . $page_output_next;
}
 
// Write the outputs
echo $line_output;
echo $page_output;
 
?>

A few points worth taking note of:

Row counting

To get the total number of results, I have used

SELECT SQL_CALC_FOUND_ROWS

followed by a second query

SELECT FOUND_ROWS() AS total

As stated in the comments, this will return the number of results that there would have been without a limit clause.  There are other ways to achieve this, namely using count() in a second query, but this way is apparently quicker, and also slightly cleaner code.

Building the paging links

In the code I have used

$_GET['rs']

What this does is get the value from the part of the URL that looks something like http://www.yoursite.com/index.php?rs=10

That value then becomes our next starting point, and is injected into the SQL query.

I’ve seen some tutorials where page numbers are used instead of starting records.  This is fairly easy to achieve, and involves dividing the number of records returned by the size of the desired result set to get the number of pages, and then multiply again when determining the next starting point for the limit.  I’ve not done that in this tutorial for the sake of simplicity.  Besides, Google uses the records, and not pages, method.  Can’t be that terrible

Extending the functionality

In this example I’m echoing the result to screen.  You could instead wrap this up in a function and return the results.  Another easy modification would be to alternate the background colours, as shown in my previous howto.

And that’s it for today.  If you found this useful, of would like to improve it, comments are always appreciated!

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Sources of inspiration

Browsing around the other day I came across Komodo Media.  Wow.  What a stunning site and awesome source of inspiration.  Rogie King, maintainer, showcases his talents in a remarkably eye-catching way.

Rogie goes the extra mile by nicely commenting his source code, so aspiring web geeks like me can learn from those who evidently know what they’re doing.

Be sure to play with the foliage-o-meter.

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PHP howto - Alternating background colours for table rows

Often when writing something for the web, you’ll need to output data in a table (or, for CSS zealots, nicely formatted <div>’s).  In order to improve readability, you might want to colour every second row differently. This is really easy:

$counter = 1;
while($counter < 10) {
 
    //set bgcolor
    $bgcol = ($counter % 2 == 1) ? "#ececec" : "#ffffff";
 
    //write the output html
    echo "<tr><td bgcolor=\"".$bgcol."\">Your content goes here...</td></tr>";
 
    //increment the counter
    $counter++;
}

The above code is merely to illustrate the idea behind alternating rows.  I’ve used a very short conditional that checks if the current row is even or odd.  Based on that result, it sets the background colour variable to either #ffffff or #ececec.  Once the loop has run, the counter is incremented, and we start over.

By the way, the line:

    $bgcol = ($counter % 2 == 1) ? "#ececec" : "#ffffff";

is equivalent to using:

    if ($counter % 2 == 1) {
        $bgcol ="#ececec";
    }
    else {
        $bgcol = "#ffffff";
    }

Some extensions to make this code better are things like inserting real data (from a call to a database), replacing the table code with <div>’s, replacing the bgcolour values with a particular style class, and writing to a string/file/etc instead of echoing the results.  Another cool thing (if in a user-based environment) is to add a subsequent if statement that checks to see if the row being processed matched the currently logged on user - this way you can show a user that the row in question belongs to them by defining a third bg colour and highlighting it differently to the rest.

A slightly more real-world example of how the code may look is:

$sql = "SELECT id, name, surname FROM person";
$result = mysql_query($sql);
$counter = 1;
 
while($row = mysql_fetch_array($result)) {
 
    //set class
    $classname = ($counter % 2 == 1) ? "dark-div" : "light-div";
 
    //write the output html
    echo "
        <div class=\"".$classname."\">
            <div>". $row['id'] ."</div>
            <div>". $row['name'] ."</div>
            <div>". $row['surname'] ."</div>
        </div>";
 
    //increment the counter
    $counter++;
}

And in next week’s issue, how to assemble a nuclear bomb from ordinary household items!

Posted in General | 5 Comments »