Think\Db\Query::parseSqlTable PHP Method

    public function parseSqlTable($sql)
    {
        if (false !== strpos($sql, '__')) {
            $prefix = $this->prefix;
            $sql = preg_replace_callback("/__([A-Z0-9_-]+)__/sU", function ($match) use($prefix) {
                return $prefix . strtolower($match[1]);
            }, $sql);
        }
        return $sql;
    }