分组依据并添加列

问题描述

我有一个名为"ward_councillors"的表以及两列"ward"和"councillor".该表包含所有议员和他们所负责的病房的列表.每个病房都有三名议员，而我需要做的是分组，以便我为每个病房拥有一个不同的记录，并在三个新的栏目中各负责该病房的三名议员.

I have a table named 'ward_councillors' and two columns 'ward' and 'councillor'. This table contains a list of all of the councillors and the ward they are responsible for. Each ward has three councillors and what i'd need to do is group by so that I have one distinct record for each ward and three new columns with the three councillors responsible for that ward in each.

例如当前具有:

WARD   | COUNCILLOR
ward a | cllr 1
ward a | cllr 2
ward a | cllr 23
ward b | cllr 4
ward b | cllr 5
ward b | cllr 8

试图实现:

WARD    | COUNCILLOR 1| COUNCILLOR 2| COUNCILLOR 3
ward a  | cllr 1      | cllr 2      | cllr 23
ward b  | cllr 4      | cllr 5      | cllr 8

预先感谢，克里斯

推荐答案

我倾向于使用条件聚合来处理这种类型的查询:

I tend to approach this type of query using conditional aggregation:

select ward,
       max(case when seqnum = 1 then councillor end) as councillor1,
       max(case when seqnum = 2 then councillor end) as councillor2,
       max(case when seqnum = 3 then councillor end) as councillor3
from (select wc.*,
             row_number() over (partition by ward order by councillor) as seqnum
      from ward_councillors wc
     ) wc
group by ward;

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