Question

使用SQL查询，我们如何获得2列的输出，第一列是以asc顺序排序的列，第二列是desc顺序，两者都是相同的列。

例如：

emp table:
empid
1 
5
9
4

查询输出应为

empid_1   empid_2
1          9
4          5
5          4
9          1

到目前为止OP尝试了什么

WITH emp1 
     AS (SELECT ROWNUM a, 
                empno 
         FROM   (SELECT empno 
                 FROM   emp 
                 ORDER  BY 1 ASC)), 
     emp2 
     AS (SELECT ROWNUM b, 
                empno 
         FROM   (SELECT empno 
                 FROM   emp 
                 ORDER  BY 1 DESC)) 
SELECT emp1.empno, 
       emp2.empno 
FROM   emp1, 
       emp2 
WHERE  emp1.a = emp2.b;

Answer 1

您可以使用row_number()和自我加入：

执行此操作

select e1.empid as empid_1, e2.empid as empid_2
from (select e.*, row_number() over (order by emp_id) as seqnum
      from emp e
     ) e1 join
     (select e.*, row_number() over (order by emp_id desc) as seqnum
      from emp e
     ) e2
     on e1.seqnum = e2.seqnum;

编辑：

您也可以使用rownum执行此操作，但需要额外的select：

select e1.empid as empid_1, e2.empid as empid_2
from (select e.*, rownum as seqnum
      from (select e.* from emp e order by empid asc) e
     ) e1 join
     (select e.*, rownum as seqnum
      from (select e.* from emp e order by empid desc) e
     ) e2
     on e1.seqnum = e2.seqnum;

Answer 2

如果使用公用表表达式/子查询分解子句，则只需访问该表一次：

with the_data as (
 select empid
      , row_number() over ( order by empid ) as id_asc
      , row_number() over ( order by empid desc ) as id_desc
   from emp
        )
select a.empid as empid_asc
     , d.empid as empid_desc
  from the_data a
  join the_data d
    on a.id_asc = d.id_desc

如何按asc顺序和desc顺序对同一列进行排序

2 个答案: