SQL如何按顺序重新排列列（从大到小）

Question

我有一个[产品]表，用于产品和利润。我需要确保MG1> MG2> MG3> ...> MG9 如何以更简便的方式重新排列此列？

尝试使用If else和case并以很长的代码结束。 非常感谢。

Answer 1

您可以取消透视和重新聚合。这是一种方法：

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如果您使用的是SQL Server或其他支持横向联接的数据库，那么最好的方法是：

select id, sku,
       max(case when seqnum = 1 then mg end) as mg1,
       max(case when seqnum = 2 then mg end) as mg1,
       . . . 
       max(case when seqnum = 9 then mg end) as mg9
from (select i.*, row_number() over (order by mg desc) as seqnum
      from (select id, sku, mg1 as mg from t union all
            select id, sku, mg2 as mg from t union all
            . . .
            select id, sku, mg9 as mg from t 
           ) i
      where mg is not null
     ) i;

在子查询中执行select t.id, t.sku, v.* from t cross apply (select max(case when seqnum = 1 then mg end) as mg1, max(case when seqnum = 2 then mg end) as mg2, . . . max(case when seqnum = 9 then mg end) as mg9 from (select mg, row_number() over (order by mg desc) as seqnum from (values (t.mg1), (t.mg2), . . ., (t.mg9) ) v(mg) where mg is not null ) v ) v; 与在外部查询中进行group by相比，具有很大的性能优势。

Answer 2

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