Building a Fair and Convincing Banner Rotator

I have seen several tutorials how to write a banner rotator online. They are technically correct but looks like the programmers haven't really put their rotators in real environment. They assume that selecting a random banner from the list (or database) will do the work and show the banners equally. Good idea and correct in general.

But as I have run such a rotator in a live site where more than 7-8 banners were rotating, I know this isn't a good enough solution. Why so? Although computer random algos or the SQL RAND() ensure all banners will be shown almost the same number of times in the long run, during 10-20 page refreshes you can keep getting the same 3-4 banners and other ones may not appear at all. This is a problem because the clients who purcased banners complain "Hey, I refreshed more than 10 times and my banner isn't showing even once!!!". Go explain them about random computer algos and that someone might be seeing their banner at the same in some other computer at the other side of the globe.

To avoid such problem, we need not only fair, but also convincing banner rotator - such that will show you the banners equal times when you are refreshing the page.

Let's see what we need:

1. A list or DB table of banners
2. Fair selection
3. Counting the views and clicks

That's in short. We will write two PHP scripts - one will select and output the banner (we'll assume you'll put it in an iframe or will add some other useful stuff to it so you can have a full page with content); and one will redirect the visitors to the targed URL and count the clicks. Let's start:

1. A list of banners

Because we need to save the number of clicks to our banners we'll use a MySQL DB table:

Table banners:
image VARCHAR(255) NOT NULL,

In the real life you will probably have also a field for customer name, email etc. but let's not worry about this now.

2. Fair selection
This is the most interesting part. Let's call our script rotator.php. It will need not only to select a supposingly random banner, but to ensure that the rotation will be equal even for every single user who is seeing the page. Here's how to do this: we will store the IDs of the banners shown in a session. When selecting, we will make sure we get a random banner from those which have not been shown yet. When all the banners have been shown once in the current session, we'll empty the data and start over. Let's talk code:


// in this array we'll store the shown banners
if(!isset($_SESSION['banner_ids'])) $_SESSION['banner_ids']=array(0);

// let's built the conditional SQL now

// now select random banner instead of these that were shown
$q="SELECT * FROM banners WHERE id NOT IN ($id_sql) ORDER BY RAND() LIMIT 1";

// enter this banner ID in the already seen ones

// now we need to check whether all the banners were shown once
$q="SELECT COUNT(id) FROM banners";

// we use "<" because our session array always contains one more ID - the zero which is
// there to prevent mysql error
if($num_banners[0] < sizeof($_SESSION['banner_ids']))

// that's it! now just display the banner:
echo "<a href='go.php?id=$banner[id]'><img src='$banner[image]'></a>";

Counting the views and clicks
Now this is pretty straightforward:


// prevent hacking
if(!is_numeric($_GET['id'])) exit;

// select banner
$q="SELECT * FROM banners WHERE id='$_GET[id]'";

// update clicks
$q="UPDATE banners SET clicks=clicks+1 WHERE id='$banner[id]'";

// redirect
header("Location: $banner[url]");

That's all!


Designing a database for a personality quiz script

Since Blogger does not offer categories, I'll have to use tags for posts like this. And what's special about it? I'm not going to talk PHP this time - instead of that I'll talk databases.

Let's discuss a database for a personality quiz script - you know, one that will build tests which will say "you are a good worker", "you like to spend too much money", "you are a loving person" etc.

What is specific for the personality quizzes? The main part is that answers to questions must be matched to personality types. Some quizzes use point systems but they are less accurate because you may have answers for contrary personality types and the system may calculate that you belong to the middle one. For personality quizzes a lot more accurate is a system which will directly match the answer to the specific personality type and at the end show the personality type which collected the most answers.

So here is my proposition for a database along with short explanations:

Table Quizzes:
title VARCHAR(255)
description TEXT

This table will contain one record for each quiz you want to run. You may want to add extra columns like date, tags etc. In num_users we will store the number of users who took the quiz.

Table Questions:
quiz_id INT UNSIGNED FOREIGH KEY to quizzes.id
question TEXT

This obviously is the table with questions. We need a foreign key to the table with quizzes and of course a field for the question itself. If you plan to have single choice and multiple choice questions, the field question_type will store the difference.

Table Answers:

quiz_id INT UNSIGNED FOREIGH KEY to quizzes.id
question_id INT UNSIGNED FOREIGH KEY to questions.id
answer TEXT
result INT UNSIGNED FOREIGH KEY to results.id

The table will have foreign keys to both Quizzes and Questions table. I know giving a key to Questions is logically enough, but I always prefer to have all the relations explicitly given in the table. This gives a lot more clarity especially if you are using ER diagrams.
The "result" column may contain things like A, B, C which will

Table Results:
quiz_id INT UNSIGNED FOREIGH KEY to quizzes.id
description TEXT

This is the last table you need. It will contain the personality types. And because the Answers table has a foreign key to it, it will be very easy to calculate which result (personality type) has the most answers given.

I'm leaving the PHP or other language implementation of this DB to you. If you want to check such thing in action, check out this php quiz script.


Easy PHP Date Picker

There are many fancy javascript calendars for selecting dates - for example the one that comes as a jQuery plugin is really cool. There are however some disadvantages to using such calendars:

  • If you only need a date picker, it's not worth to include all these Javascript libraries and overload.

  • These javascript calendars are hard to use from people who don't see well or can't use a mouse

  • In admin screens etc., where you may need to manage many dates in rows of records, clicking on the calendars can be much slower than picking dates from dropdown.

In cases like these and maybe more, it's better to create a simple dropdown date picker that will allow the user to select year, month and day (in fact this will be 3 dropdowns).

Let's build such a function:

First we'll build an array of months:


Note that I inserted the first element of the array as empty because I want the month numbers to start from 1 (for January).

Then we'll construct the three dropdowns:

$html="<select name=\"".$name."month\">";
$html.="<option value='$i'>$months[$i]</option>";
$html.="</select> ";

This was the months dropdown. Did you notice the "name" variable? We will pass it as argument to the function so we can control the name of the dropdowns and have many of them in a page. In very similar way you can create the days dropdown - from 1st to 31st.

$html.="<select name=\"".$name."day\">";
$html.="<option value='$i'>$i</option>";
$html.="</select> ";

The years dropdown is just as simple. The only question in it is in what year to start and when to end. Your function can accept this as arguments or you can dynamically create start and end year accordingly to the current date. For example:

$startyear = date("Y")-100;
$endyear= date("Y")+50;

$html.="<select name=\"".$name."year\">";
$chooser.="<option value='$i'>$i</option>";
$html.="</select> ";

You can add some javascript to increase/reduce the number of days accordingly to the month, but this can be needlessly complicated. It's easier to solve this problem by javascript validation at the time when the form is submitted.

So Here Is The Full Code (For Those Who Don't Get It):

Then put all this code into a function which accepts the argument $name:

function date_picker($name, $startyear=NULL, $endyear=NULL)
if($startyear==NULL) $startyear = date("Y")-100;
if($endyear==NULL) $endyear=date("Y")+50;

'June','July','August', 'September','October','November','December');

// Month dropdown
$html="<select name=\"".$name."month\">";

$html.="<option value='$i'>$months[$i]</option>";
$html.="</select> ";

// Day dropdown
$html.="<select name=\"".$name."day\">";
$html.="<option $selected value='$i'>$i</option>";
$html.="</select> ";

// Year dropdown
$html.="<select name=\"".$name."year\">";

$html.="<option value='$i'>$i</option>";
$html.="</select> ";

return $html;

And use the function as echo date_picker("registration") (for example - "registration" is just a name you choose). The result that will come in $_POST after submitting such form will be in 3 variables:
$_POST['registrationmonth'], $_POST['registrationday'] and $_POST['registrationyear'].

You can easily construct a MySQL date from these variables.

Now think how you can make this dropdown read stored data and pre-select its values accordingly to it (for "Edit record" forms).


Building a Simple Monthly Calendar

In this tutorial we are going to learn how to build a simple calendar in PHP. You have seen many of those calendar date pickers mostly in Javascript. This PHP based one has a slightly different purpose - instead of populating an input field, it outputs links for the different dates and can be used for example as a monthly archive in a dynamic DB-driven site.

We will build this calendar following good coding practices and keeping the login in one PHP file and the presentation in one HTML file.

Let's start:

First we need to define the current date OR a date coming by POST after the calendar form is submitted:


PHP getdate() function returns an array of year, month and day. We assign this to $today variable and use it to define the calendar day, year and month - if they are coming from POST, the POST values have priority - otherwise we use $today values.

Then we need to define the number of days in the given month. We use function cal_days_in_month() for that:

$numdays=cal_days_in_month(CAL_GREGORIAN, $month, $year);

Now there's one specific. We don't want the calendar rows to be different number in different month. For that we'll make sure the calendar looks like the printed calendars and like this event calendar software by defining the week start day:

// calculate 'extra' days - these which need to come on the first
// line - like 30-31- -- - -- - -- - -- - 1

That's it, now we only need to include the design template:


The rest is easy - display year and month dropdows:

<select name="year" onchange="this.form.submit();">
if($i==$year) $selected='selected';
else $selected='';
echo "<option $selected value=$i>$i</option>";
<select name="month" onchange="this.form.submit();">
if($i==$month) $selected='selected';
else $selected='';
echo "<option $selected value=$i>".$lmonths[$months[$i]]."</option>";
// end PHP

And the calendar itself in a HTML table:

if($extra<0) $extra=0;
// ...
// the full code can be downloaded at the bottom

And your calendar is ready! You can download the free Microcal script that uses this same code here

Welcome... and first few tips!

Welcome to my new blog featuring some of my PHP tutorials. Here I'll try to share simple and elegant hacks that will help you not only solve varios problems but solve them in easier, quicker and more elegant way.

Being a great PHP developer doesn't mean to know each and every function and feature of the language. It means to solve the real world problems in efficient way. This is what the blog is going to help you for.

Let's start with a few random smart tips

  • Using the alternate PHP syntax in the HTML code will make it much cleaner and easier to follow.

  • Make your own database object or download a class online instead of using the PHP built-in functions like mysql_query etc. It's not that you are going to change the DB engines (it's unlikely) - it's about using far more comfortable functions that return directly arrays of objects of the results you are selecting.

  • Don't forget about the HEREDOC syntax.

  • When passing IDs in the URL check them with is_numeric() function. In many cases this is all you need to avoid attacks.

  • Use good PHP editor such as CodeLobster.

  • Put a small comment at the beginning of all your PHP files. This is extremely useful when you return to old code.

  • Use variable names that make sense. For example when selecting users from the DB call the result array $users instead of $rows. This will help you when the variable appears 10 lines later.

These tips are very basic, but I promise that's just the start. There are a lot more useful things coming in place here. Stay tuned!