1、将排序后的查询结果拼接起来
select * from(select  *  from table order by a)

union

select * from (select * from table1 order by b)

union

select * from (select * from table2 order by c);

2、将排序后的查询结果拼接起来,再排序

select * from(select  *  from table order by a)

union

select * from (select * from table1 order by b)

union

select * from (select * from table2 order by c)

order by d;----此处的order by 是将最后的拼接结果集排序  打乱了之前通过 a、b、c的排序。
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作者:搬长城的红砖