How to get my data back

I am new to dynamic data and trying to

1. Read data from mysql database using PHP
2. Convert this data to JSON
3. Extract data via javascript (jQuery)
4. Insert it into my page.

As far as I can tell, 1) and 2) work, 3) seems to work, and 4) solves the problem.

I have set up the database and tables, querying and echoing the data like this (api.php)

<?php 

  include 'db.php';
  $con = new mysqli($host,$user,$pass,$databaseName);

  /* check connection */
if (mysqli_connect_errno()) {
  printf("Connect failed: %s\n", mysqli_connect_error());
  exit();
}

  $query = "SELECT * FROM $tableName";
  $myArray = array();

  if ($result = $con->query($query)) {
    $tempArray = array();
    while($row = $result->fetch_object()) {
      $tempArray = $row;
      array_push($myArray, $tempArray);
    }
    echo json_encode($myArray);
  }

  $result->close();
  $con->close();

?>

Now I get it via javascript...

jQuery(function($) {    
    $.ajax({                                      
        url: 'php/api.php',
        data: "json",
        dataType: "",    
        success: function(data) {
            var r = new Array(), j = -1;
            for (var key=0, size=data.length; key<size; key++){
                r[++j] ="<tr><td>";
                r[++j] = data[key][0];
                r[++j] = "</td><td>";
                r[++j] = data[key][1];
                r[++j] = "</td><td>";
                r[++j] = data[key][2];
                r[++j] = "</td></tr>";
            }
            var joined = r.join('');
            console.log(joined);
            $('#maintable tbody').html(joined);    
        }
    });
});

...and throw it into the tbody element of my table.

The result is definitely not what I expected:

See http://i.imgur.com/hRNrmdC.jpg (sorry for some german interface)

The answer to the GET request is at least theoretically valid JSON ( checked with http://jsonlint.com/ ), but to me the data seems to be treated as a string and split into an array of chars (each char a "key" in data[], so "data[key][1] returns nothing.

var json = JSON.stringify(eval("(" + data + ")"));

and keep using json[key][0] doesn't help...

Now, I want to know why, especially where is the problem and how to fix it .