<?php
$sdbhost = 'dbhost';
$dbuser = 'dbuser';
$dbpass = 'dbpassword';
$conn = mysqli_connect($dbhost, $dbuser, $dbpass, $dbuser);
if (!$conn){
    die('cannot connect to mysql');
}



$query = "SELECT `entry1` FROM `$selectedTable` WHERE 1 LIMIT 0, 30 ";

if ($result = mysqli_query($conn , $query)) {

    $num = mysqli_num_rows($result);

    for ($i = 0; $i < $num; $i++){

        $myArray[] = mysqli_fetch_assoc($result);

    }
    echo "<div class = 'dataSelect'>";

    foreach( $myArray AS $key=>$data ){

        echo "<input type='checkbox' name = '". $data['entry1'] . "' value = '".$data['entry1']."'> " .$data['entry1']. "<br/>";
    }

    echo "</div>";


}else{
    echo "Something wrong";
}


?>

var checkedAttr = [];

//Everytime checkbox is changed
$('input:checkbox').change(function(){
    //Everytime Checkbox is checked
    if ($(this).is(':checked')) {
        $(' input:checkbox').each(function(i, item){
            if($(item).is(':checked')){
                //Add into Array
                checkedAttr.push($(item).val());
            }
        });
    }
    var jsonString = JSON.stringify(checkedAttr);
    console.log(jsonString);

    // AJAX to PHP
    $.ajax({
            type: "POST",
            url: "dataToGraph.php",
            data: { data : jsonString },
            cache: false,
            success: function(){
                alert('Okay');
        }
    });
    //Prevent more than two rows selected
    if ($('input:checkbox:checked').length >= 2) {
        $(".dataSelect").fadeOut('slow');
    }
});

<?
   if(isset($_POST['data'])){
      $data = $_POST['data'];
      print_r($data);
      foreach($data as $d){
        echo $d;
      }
   }else{
       echo'SOMETHING IS WRONG WITH THIS, DON'T BE SADDDD';
   }
?>