json success function not executing - php

Question

I am trying to post value of an input box and a obtain value of the checked radio button and perform a query based on which radio button is checked ... but my success function is not executing...
Html form :
<form class="form-inline" id="myForm">
<label class="radio">
<input type="radio" id="title1" name="title" value="title">
Title
</label>
<label class="radio">
<input type="radio" id="author" name="title" value="author">
Author
</label>
<label class="radio">
<input type="radio" id="subject" name="title" value="subject">
Subject
</label><br>
<input type="text" name="input"> </input>
<button class="btn btn-inverse" id="download" >Go</button>
</form>
jQuery :
$('document').ready(function(){
$('input[name=title]:first').attr('checked', true);
$('#download').click(function(){
value = $('input[name=title]:checked', '#myForm').val();
alert(value);
var input = $('#input').attr('value');
dataString = 'title='+ value +'&input='+input;
wurl = "downloadE.php";
$.ajax({url: wurl, type: "POST",dataType: "json",data:dataString ,success: function(data){
alert("success");
}
})
})
});
php code:
$value = $_POST['title'];
$output = $_POST['input'];
if($value=="title")
{
$query = " select * from library where Title = '$output'; ";
}
else if($value=="author")
{
$query = " select * from library where Author = '$output'; ";
}
else if($value=="subject")
{
$query = " select * from library where Subject = '$output'; ";
}
$result = mysql_query($query);
$ret = array();
while($info = mysql_fetch_array( $result )){
$ret[] = $info;
}
echo json_encode($ret);

Answer 1

When I encounter these types of issues, I'll add an error function and output the details to the console log so that it will help figure out the error. Like so:
,success: function(data){
alert("success");
},error: function(e){
console.log(e);
}

Answer 2

Try this
var callback = function( resp ) {
alert(123);
}
$.post(url, data, callback, "json");

Answer 3

<input type="text" name="input"> </input>
is wrong, and you're missing an ID I believe:
<input type="text" name="input" id="input" />
You also need to check that your script is executing. If nothing is being return in your JavaScript it means that the script is failing on the server side.