1.php

<?php
    /**
     * @return string
     */
    public function getDefault(): string
    {
        if (is_numeric($this->default)) {
            return $this->default;
        } elseif (strtoupper($this->type) === 'TIMESTAMP' and $this->default = 'CURRENT_TIMESTAMP') {
            return $this->default;
        } else {
            return "'$this->default'";
        }
    }