no results in inserting values to MySQL with AJAX - php

Question

on my research site, I have a few radio buttons and I want to send their values to MySQL table using jquery and AJAX. All buttons and jquery code are put in single-project.php (I modified WordPress theme) and the bits of code that should handle interaction with the MySQL are put in the db.php in the same folder.
However, something is not in order, because values do not appear on the database table. Could someone help?
jquery:
//the last button
$('#submit_last_button').click(function(){
SomeVariable = $('input:radio[name=lastRadio]:checked').val();
if (!$("input:radio[name=lastRadio]").is(":checked")) {
$("label#lastRadio_error").show();
$("input#lastRadio").focus();
return false;
} else {
if ('input:radio[name=lastRadio]:checked')
$('#PreviousButtonDiv').hide();
$('#NextDiv').show();
$.post('db.php',{action: "submit_last_button", previous_variable:SomePreviousVariable, last_variable:SomeVariable},function(res){
$('#result').html(res);
});
}
});
});
db.php:
<?php
$con = mysql_connect('localhost','user', 'password');
$db = mysql_select_db('my_database');
if($_POST['action'] == 'submit_last_button'){
$previous_variable = mysql_real_escape_string($_POST['previous_variable']);
$last_variable = mysql_real_escape_string($_POST['last_variable']);
$sql = "insert into MyTable (id, variable1, variable2) values ( NULL, '$previous_variable', '$last_variable')";
$query = mysql_query($sql);
if($query){
echo "Record Inserted.";
}else {
echo "Something Wrong!";
}
}
?>

Answer 1

There are various possibilities of what is not working on your code. But first, the problem is not in AJAX not saving on MySQL. AJAX is passing your data to the php script on your server to then, save it on MySQL.
Check if the values are reaching your script correctly;
Check if you're getting a db connection - check error logs or print them out;
Check if you're not getting a SQL syntax erro - again, check for logs;
Check if auto-commit is true (it is by default).