I'm trying to increment a php variable with the click of a html button and then call a php function wich uses this variable as a parameter.
The html code simply has two buttons that increase or decrease the current date. When I click on the increase button, I want my $day variable to be increased, passed to the getFromDB($day) function and then run the getFromDB($day) function again.
I've read that I should use ajax for that but I simply don't understand how that would work on the same page. (Also please no form with page reload)
Here's the html code with the 2 buttons
<div class="row dateTitle">
    <div class="col" style="text-align: center; font-size:2em;">
       <button id="prevButton" style="outline:none; background:none; border:none;">
                <  </button> <span id="setDate">15.01.2011</span> <button id="nextButton" style="outline:none; background:none; border:none;">  ></button>
     </div>
</div>
Here is my php function
 <?php
        function getFromDB($day){
        if(!isset($day))
        {
           $day = jddayofweek($julianday [0]);
        }
        $servername = "localhost";
        $username = "****";
        $password = "*****";
        $dbname = "***";
        // Create connection
        $conn = new mysqli($servername, $username, $password, $dbname);
        // Check connection
        if ($conn->connect_error) {
            die("Connection failed: " . $conn->connect_error);
        } 
        $dayOfWeek = $day; //jddayofweek($julianday [0]);
        $sql = "SELECT * FROM `courseTimes` JOIN courseNames ON courseTimes.nameID = courseNames.ID WHERE dayOfWeek = " . $dayOfWeek;
        $result = $conn->query($sql);
            if($result->num_rows > 0) {
             while($row = $result->fetch_assoc()){
                echo '<tr>
                    <th scope="row">' .$row["startingTime"]. ' - ' .$row["endingTime"]. '</th>
                    <td style="background-color: rgb(226, 194, 145);">' .$row["cName"]. '<button
                            class="tableButton" onclick="openModal()">(Anmelden)</button></td>
                </tr> ';
             }
            }
         $conn->close();
        }
        getFromDB();
    ?>
The button should simply call the getFromDB($day) function , similiar to the onclick event with javascript.