Tutorial: How to build a poll system with PHP and mySQL
So we now have a form that displays the template of our poll. What we need now is a way to save the user selections so that we can calculate the votes. We will be storing the user votes along with their IP Addresses in the mysql database. This gives us the advantage of limiting one vote per user, well yes, one vote per IP Address.
If you are building this into your website, you might want to use user id's instead, limiting the access to only registered users. This would mean that a brother and a sister could both vote their opinion whilst using the same IP Address, as they would both have two different user names. As we are not integrating this polling system into a community system, we will happily use our IP Address system. We will be using the index.php file to handle this section, because its neater at the moment!
7. Open up your index.php file and underneath the include('config.php') statment add this:
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$query = mysql_query("SELECT `questions`.`pid` FROM `responses`, `questions` WHERE `responses`.`qid`=`questions`.`id` AND `responses`.`ip`='".$_SERVER['REMOTE_ADDR']."' AND pid=(SELECT pid FROM `questions` WHERE id='".$_POST['questions']."' LIMIT 1)");
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$query = mysql_query("INSERT INTO `responses` (`qid`, `ip`) VALUES ('".$_POST['questions']."', '".$_SERVER['REMOTE_ADDR']."')");
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} else {
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$error = 'You Already Voted';
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}
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$error = 'You Need To Select a Question';
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}
Let's have a look at the code (*drinks coffee*).
This line examines the actions of the user. First it checks if the submit button has been pressed by looking for its contents. It also checks that a question has been selected. If both of these are present, then that means someone has selected an option and that the form has been submitted. So our next task is to check if that person has voted before. This is done via this line:
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$query = mysql_query("SELECT `questions`.`pid` FROM `responses`, `questions` WHERE `responses`.`qid`=`questions`.`id` AND `responses`.`ip`='".$_SERVER['REMOTE_ADDR']."' AND pid=(SELECT pid FROM `questions` WHERE id='".$_POST['questions']."' LIMIT 1)");
This query is quite massive. It is because we separated our questions from our polls. I will explain how it works, from right to left. First we need to get the parent id of our question. If we didn't we would merely be testing if that particular question was submitted, and in turn, a user could submit a vote for each and every question. So we need to search if the user has submitted an answer to the poll, as apposed if the user has submitted just a question before. So once when have the pid (poll id) of the we need to see if the user ip already exists in the reponses table.
After that we join the questions table and the responses table so that the responses table also gets the poll id so we can cross match, which was done when we compared the submitted question against the pid and the questions pid. Confusing! I know!
Lets proceed,
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$query = mysql_query("INSERT INTO `responses` (`qid`, `ip`) VALUES ('".$_POST['questions']."', '".$_SERVER['REMOTE_ADDR']."')");
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} else {
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$error = 'You Already Voted';
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}
This section tests if there was a result from the previous SQL statement, i.e. if an ip address already exists for the given poll. If there was no IP in the table then it continues to post the user's response. If the ip was already found we put some text into a variable called $error;
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$error = 'You Need To Select a Question';
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}
Here we catch any users who clicked the submit button but did not choose an option to vote for. We also add this to the $error variable.
So now we have reponses going into our database, its time to go back to poll.php to handle the calculations and any errors!
17 Responses to “Tutorial: How to build a poll system with PHP and mySQL”
By Cristi
on Jun 11, 2008
It would be perfect if it had a form to add the question and a form to edit them. Anyway Good Job.
By VoiDeT
on Jun 11, 2008
Yep sure.
You should take the guestbook tutorial and build that feature yourself! It is not hard at all
By chor khee
on Jul 16, 2008
nice one man! just a simple question. Can this be done using jsp and mYsql? are there any links for that?
By VoiDeT
on Jul 16, 2008
Hey Chor Khee,
I don’t know JSP, sorry.
Have fun with the port!
By Ana
on Jul 25, 2008
Thank you very much it really is great, it gave me the whole picture. I am using Access data base, how can I use this nice piece of code for Access. Thanks again.
By Hunter
on Aug 11, 2008
Hi,
I downloaded the source, and uploaded it in tact, minus editing in my database information.
I get this error:
http://www.nineprinces.org/hunter/php/tutorials/
”
Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home/backline/public_html/hunter/php/tutorials/poll.php on line 4″
What’s up w/ that?
By Hunter
on Aug 11, 2008
Nm, fixed it
By VoiDeT
on Aug 11, 2008
And how did you fix it?
By Hanayo
on Sep 24, 2008
I tried working on it but I as totally lost when it came to the whole phpmyAdmin thing??
I couldn’t figure out what you were talking about the click Insert or whatever since I didn’t see that anywhere on my page…
Like I know how to read html/css fairly well and can read xhtml. But php is what I’m learning, and so i know i put the codes in all the right spots but I don’t know what you meant by that and I tried but I dont’ think i got it…
http://www.aestheticloveinc.com/poll/index.php and it’s just blank….
By blckheart
on Sep 25, 2008
RE: And how did you fix it? Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in
To fix the error, you will have to connect to the database. In the downloaded files there is no config.php file or db.inc file to connect to the database, therefore the mysql_num_rows cannot find any info from the database, because there is no connection to the database. Or at least this is what happened in my case.
To connect to the database use the following code in the poll.php file or create a seperate config.php file and just use an include ‘config.php’; or require ‘config.php’; in the top of your poll.php file
//Connection to Database
$hostName = “localhost”;
$databaseName = “yourdatabasename”;
$databaseusername = “yourdbusername”;
$dbpassword = “yourdbpassword”;
$connect = @mysql_connect($host, $yourdbusername, $yourdbpassword);
if (!mysql_select_db($databaseName, $connect))
echo ‘Could not connect to database’;
I hope this helps, i dont know why someone would ask for help on the error and then say he fixed it without giving a solution, he has the time to ask but not the time to help, i think that sucks!
By VoiDeT
on Sep 27, 2008
blckheart what do you think is sitting in the root folder? would it be a config.php file by anychance? With this code in it?
< ?php
//database settings
$hostname = 'localhost';
$username = 'yourusername';
$password = 'yourpassword';
$dbname = 'poll';
$connect = mysql_connect($hostname, $username, $password);
mysql_select_db($dbname);
?>
Look at the files.
By BlueDevil18
on Sep 28, 2008
I set everyhing up. Added a New Poll and Questions to the poll with the correct pid. However, when I browse to the file(poll.php) on the server, it still comes up “No Poll Yet” Am I not doing something?
By BlueDevil18
on Sep 28, 2008
I need some help with this. I think i set up up correctly, but i still get “no poll yet”
By Rkrueger
on Oct 12, 2008
hey i was doing this and it came up with the error that the function “max()” doesn’t have enough parameters..
can someone check this out?
By Hodde
on Oct 28, 2008
I get the “no poll yet”-message too.. and i’m also pretty sure i set the poll up correctly..
By Stonedeft
on Dec 13, 2008
You should have separated codes and html. It gets real confusing I have to strip html tags the poll.php for me to review the code.
Well I got the idea but man you should recode this to for web 2.0 standards
By VoiDeT
on Dec 13, 2008
Thank you for the comment,
Maybe you could say something like, maybe you should use objects, or logic from design separation, but web 2.0 standards haha
Web 2.0 standards in php LOL