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POajax call to check duplicate data
 

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    <p>Here is the form to have ajax check out user existence.</p> <pre><code>&lt;!DOCTYPE html&gt; &lt;html&gt; &lt;head&gt;&lt;title&gt;Register new user!&lt;/title&gt; &lt;script src="jquery-1.7.1.min.js"&gt;&lt;/script&gt; &lt;/head&gt; &lt;body&gt; Username: &lt;input type="text" name="username" id="username"/&gt;&lt;span id="user"&gt;&lt;/span&gt;&lt;br/&gt; Password: &lt;input type="password" name="password" id="password"/&gt;&lt;br/&gt; &lt;input type="button" value="Register" name="submit" id="submit" onclick="register_user();"/&gt; &lt;/body&gt; &lt;script&gt; function register_user() { $.ajax( { type:"POST", data:username, url:"userexists.php" }) .fail(function() { $('#user').html("This user already exists"); } ); } &lt;/script&gt; &lt;/html&gt; </code></pre> <p>And here is the userexists.php module</p> <pre><code>&lt;?php // connection to the db define(IPHOST,"localhost"); define(DBPASSWORD,""); define(DBUSER,"root"); define(DATABASE,"ajaxtest"); define(TABLENAME,"at"); $conn=mysql_connect(IPHOST,DBUSER,DBPASSWORD) or die(mysql_error()); mysql_select_db(DATABASE) or die(mysql_error()); $username=$_POST('username'); $sql="SELECT username FROM ".TABLENAME." WHERE username=".$username; $query=mysql_query($sql); if(0!=mysql_numrows($query)) { // } else { } ?&gt; </code></pre> <p>But I am stuck to really figure out how the ajax function actually works, what should I enter the blank field after I know that the entered username has been used, for example ? I don't understand ajax at all.</p> <p>[<strong>UPDATE</strong>] Thank you, I understand it now, I have got several answers, don't know which one to choose as the best reply. No option to choose all.</p>
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    1. COThere are a lot of problems with this code. Namely, that PHP code won't even run. Turn on error reporting, fix your syntax errors, then look into SQL injection. Also, you're going to get a lot of notices when you look at the errors. You should consider googling them and learning what they mean and how to fix them.
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    2. COThere are quite a few responses, but I added a bit of an explanation on how it all works. Hope its of some use for you :)
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