union不能和order by不能共用怎么办？
如下，不行，会报错：
SELECT *
FROM person
ORDER BY t.id
UNION ALL
SELECT *
FROM person
ORDER BY t.id
但是可以折中一下，将排序后的结果集放在子查询中：
SELECT *
FROM (SELECT * FROM person ORDER BY t.id)
UNION ALL
SELECT *
FROM (SELECT * FROM person ORDER BY t.id)