checkbox checked and explode data in php/mysql

I have a problem with automatically checked values. Using a database, I display the values in a checkbox. Then from the database from another table I want to automatically select them. The data is in the list. I exploded it and checked.

<?php
    require('../config.php');
    $result = mysqli_query($con, "SELECT * FROM pk_skladnik") or die ( mysqli_error($con) );
    while($row = mysqli_fetch_assoc($result)){
        $cal = mysqli_query($con, "SELECT * FROM pk_pizza WHERE IdPizza = 1") or die ( mysqli_error($con) );
        $sol = mysqli_fetch_array($cal);
        $values = $sol['sklad'];
        $array_of_values = explode(", ", $values);
?>
<div class="form-check">
    <?php 
        foreach ($array_of_values as $key){
            $xxx = ($key == $row['skladnik'] ? "checked" : "");
    ?>
    <input class="form-check-input" type="checkbox" value="<?= $row['skladnik']; ?>" <?= $xxx; ?>>
    <?php } ?>
    <label class="form-check-label">
        <?= $row['skladnik']; ?>
    </label>
</div>
<?php } ?>

The current result is, for example, three rows of columns with one value checked in each of them. I want to check these 3 values in one column.