Vertica:如何按某种顺序连接值? [英] Vertica: how can you concate values by some order?

问题描述

假设您有列

ID | A | B | C
1  | 3 | 1 | 2
2  | 5 | 9 | 1
3  | 1 | 2 | 3 

，并且您希望将各列连接起来，以使最终结果看起来像

and you want the columns concatenated such that the end result would look like

ID | ABC_value_DESC | ABC_value_DESC_colnames
1  | 3,2,1          | A,C,B
2  | 9,5,1          | B,A,C
3  | 3,2,1          | C,B,A 

要在新列ABC_value_DESC中按降序获取col值的位置，然后在新列ABC_value_DESC_colnames中返回相应的列名.

where you want to get the col values in Descending order within the new column ABC_value_DESC and then return corresponding name of column in the new column ABC_value_DESC_colnames.

如何在Vertica 9中将多列的值按降序串联到新列中，并按值顺序(而不是名称顺序)返回列名?

Ps.我已经尝试过Listagg -function，但是却遇到无法执行排序的错误，并且尝试了Vertica的建议时

Ps. I have tried Listagg -function but bugs such that ordering not implemented and when tried Vertica's suggestion here giving false result and even bugs with alternative here.

推荐答案

您可以使用讨厌的case表达式执行此操作.对于三列来说，还不错:

You can do this with a nasty case expression. For three columns it is not so bad:

select t.*,
       (gr || ',' ||
        (case when a not in (le, gr) then a
              when b not in (le, br) then b
              else c
         end) || ',' ||
        le
       ),
       ((case gr when a then 'a' when b then 'b' else 'c' end) || ',' ||
        (case when a not in (gr, le) then 'a'
              when b not in (gr, le) then 'b'
              else 'c'
         end) || ',' ||
        (case le when a then 'a' when b then 'b' else 'c' end)
       )          
from (select t.*, greatest(a, b, c) as gr, least(a, b, c) as le
      from t
     ) t;

此特定版本假定没有重复项或NULL值，尽管可以将其用于此目的.

This particular version assumes there are no duplicates or NULL values, although this can be adopted for that purpose.

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