union all子查询排序
正确sql：
(select * from menu ORDER BY `name` limit 5)
union all (select * from menu ORDER BY `name` desc limit 5)起始SQL：
子查询分别排序，结果报错，明显是union all和order的使用有错
select * from menu ORDER BY `name`
union all (select * from menu ORDER BY `name` desc )
[Err] 1221 - Incorrect usage of UNION and ORDER BY查看资料显示，order by如果写在最后面是对整个结果的排序：
子查询1
union all
字查询2 order by......不是对子查询2的排序，想到加上括号：
(select * from menu ORDER BY `name` )
union all (select * from menu ORDER BY `name` desc )没有报错有数据，但是发现数据的顺序不是我们想要的，根本就没有排序，继续查找发现需要加limit关键字。
(select * from menu ORDER BY `menu` limit 5)
union all (select * from menu ORDER BY `menu` desc limit 5)