Db::field('name')
    ->table('think_user_0')
    ->unionAll('SELECT name FROM think_user_1')
    ->unionAll('SELECT name FROM think_user_2')
    ->select();
//->paginate(10,true,['page' => $page]);

应用场景：

获取文章，问答，资讯表合并为全部文章列表，并根据创建时间排序

union合并后去重

unionAll合并后不去重