Answer by Marc B for PHP array from checkbox values returns only Array instead of values

Given your name="cb1[]", your $_POST value will simply be $_POST['cb1'], which happens to be an array:

foreach($_POST['cb1'] as $key => $value) {   echo $value; // spit out a name   echo $_POST['cb1'][$key]; // same thing, in a different way}

Plus, as written, your query is vulnerable to SQL injection attacks.