How to change the checkbox property

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PHP

Ajax

MySQL

jQuery

In the table in the database contains the column date, checkbox. How can I disable the checkbox if the inputted date is already in the database.For example, if in the table contains date = 13/9/2019 and checkbox = h1, then if we input the date 13/9/2019, the checkbox h1 is disabled

<input type="checkbox" name="checkbox[]" id="checkbox" value="h1">
<input type="checkbox" name="checkbox[]" id="checkbox" value="h2">
<input type="date" name="date" id="date">

<?php 
$db = mysqli_connect('localhost','root','','mydatabase');
if (isset($_POST['date2'])){
$query = mysqli_query($db, "SELECT * FROM mytable where date ='".$_POST["date2"]."'");
// what to put here?
}
?>

$(document).ready(function {
  $("#date").change(function {
    var date = $("#date").val();

    $.ajax({
      url: "variable.php",
      method: "POST",
      data: {
        date2: date
      },
      dataType: "text",
      success: function(html) {
        //what to put here?
      }
    });
  });
});

What I have tried:

I have tried to echo checkbox val, but no luck