Question

I want to return JSON data from a resulted SQL statement in a PHP script upon pressing Submit button, but I receive null instead.

I’ll be using the returned JSON to filter-show markers on my Google Map, but for now I just want to get the data back across to my jQuery page from PHP script so I can manipulate/use it.

Submit button:

HTML

<input type="submit" id="filter" value="Filter" />

JS

$('#myform').on('submit', function(e) {
  e.preventDefault();
  var myData = $('#myform').serializeArray();
  $.getJSON('myscript.php', myData, function(json){
    alert(json);// actually filter for later                    
  });   
});

PHP script:

// action is a hidden form control I use to check if form was submitted
    if(isset($_POST["action"])){

        if(isset($_POST["color"]) && isset($_POST["zipcode"])){
            // try to open a connection to a MySQL server
            $connection = mysql_connect($host, $username, $password) or die("Could not connect" . mysql_error());
            // select the active MySQL database to work with
            $db_selected = mysql_select_db($database, $connection) or die("Can\'t use db:" . mysql_error());

            $query = 'sql statement to return resutls based on what color and zipcode was provided';
            $result = mysql_query($query) or die("Can\'t do that: " . mysql_error());
        }

        //  close connection to the database


    echo json_encode($result);
    mysql_close($connection);
    }

Answer 1

You can’t return the result object of a mysql_query call directly. You first have to parse it with functions like mysql_fetch_array or alike (PHP docu).

...
$result = mysql_query($query);
if ( $result === false ) {
  die("Can\'t do that: " . mysql_error());
}

$retVal = array();
while( $row = mysql_fetch_array( $result ) ) {
  $retVal[] = $row;
}

...
echo json_encode( $retVal );

EDIT

According to the jQuery spec for getJSON (link), the data is sent using GET parameters and not using POST. So you would have to change all the $_POST appearances in your PHP code to either $_GET or $_REQUEST.

Besides this, you should return some error messages if your variables are not set. Right now (according to your code) just an empty document is returned.