WHERE子句未显示数据

Question

我正在尝试添加WHERE子句来过滤表数据，但是它什么也没显示，它的数据表AJAX CRUD项目，任何帮助都将不胜感激 完整教程的链接：https://www.webslesson.info/2017/01/php-pdo-ajax-crud-with-data-tables-and-bootstrap-modals.html

$query = '';
    $query .= "SELECT * FROM users WHERE id = 1 ";
        if(isset($_POST["search"]["value"])) {
            $query .= 'AND first_name LIKE "%'.$_POST["search"]["value"].'%" ';
            $query .= 'OR last_name LIKE "%'.$_POST["search"]["value"].'%" ';
        }
        if(isset($_POST["order"])) {
            $query .= 'ORDER BY '.$_POST['order']['0']['column'].' '.$_POST['order']['0']['dir'].' ';
        } else {
            $query .= 'ORDER BY id DESC ';
        }
        if($_POST["length"] != -1) {
            $query .= 'LIMIT ' . $_POST['start'] . ', ' . $_POST['length'];
        }

如果我使用下面的代码，我将从表中获取所有结果

$query = '';
    $query .= "SELECT * FROM users ";
    if(isset($_POST["search"]["value"])) {
        $query .= 'WHERE first_name LIKE "%'.$_POST["search"]["value"].'%" ';
        $query .= 'OR last_name LIKE "%'.$_POST["search"]["value"].'%" ';
    }
    if(isset($_POST["order"])) {
        $query .= 'ORDER BY '.$_POST['order']['0']['column'].' '.$_POST['order']['0']['dir'].' ';
    } else {
        $query .= 'ORDER BY id DESC ';
    }
    if($_POST["length"] != -1) {
        $query .= 'LIMIT ' . $_POST['start'] . ', ' . $_POST['length'];
    }