MySQL高阶2159-分别排序两列

题目

编写解决方案，使：

• first_col 按照 升序 排列。
• second_col 按照 降序 排列。

准备数据

Create table If Not Exists Data (first_col int, second_col int)
    Truncate table Data
    insert into Data (first_col, second_col) values ('4', '2')
    insert into Data (first_col, second_col) values ('2', '3')
    insert into Data (first_col, second_col) values ('3', '1')
    insert into Data (first_col, second_col) values ('1', '4');

分析数据

a表

select row_number() over(order by first_col) as id, first_col
     from Data

b表

select row_number() over(order by second_col desc) as id, second_col
     from Data

根据关联条件将两表关联起来

select a.first_col, b.second_col
from
    (select row_number() over(order by first_col) as id, first_col
     from Data) a join
    (select row_number() over(order by second_col desc) as id, second_col
     from Data) b on a.id = b.id;

总结

如果两个表关联条件字段相同,也可以使用using(关联的字段名)

比如这道题,最后可以使用"using(id)"  代替  " on a.id = b.id "

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本题错误做法

select * from data
    order by first_col asc,second_col desc;

因为本题是单独让每列排序,而上面做法second_col的降序会在first_col升序的情况下再排序