postgresql unnest 和 pivot int 数组列

Question

我有下表

create table test(id serial, key int,type text,words text[],numbers int[] );

insert into test(key,type,words) select 1,'Name',array['Table'];
insert into test(key,type,numbers) select 1,'product_id',array[2];
insert into test(key,type,numbers) select 1,'price',array[40];
insert into test(key,type,numbers) select 1,'Region',array[23,59];
insert into test(key,type,words) select 2,'Name',array['Table1'];
insert into test(key,type,numbers) select 2,'product_id',array[1];
insert into test(key,type,numbers) select 2,'price',array[34];
insert into test(key,type,numbers) select 2,'Region',array[23,59,61];
insert into test(key,type,words) select 3,'Name',array['Chair'];
insert into test(key,type,numbers) select 3,'product_id',array[5];

我正在使用以下查询来为用户透视表。

select key,
max(array_to_string(words,',')) filter(where type='Name') as "Name",
cast(max(array_to_string(numbers,',')) filter(where type='product_id') as int) as "product_id", 
cast(max(array_to_string(numbers,',')) filter(where type='price') as int) as "price" ,
max(array_to_string(numbers,',')) filter(where type='Region') as "Region"
from test group by key

但我无法在 Pivot 期间取消嵌套 Region 列，以便使用 Region 列与另一个表连接。

我的预期输出低于

Answer 1

因为我们使用 unnest("Region") 来做枢轴。每个产品必须有一行包含区域数据。 或者下面的代码将通过创建一个空数组来解决问题。

unnest(CASE WHEN array_length("Region", 1) >= 1
                    THEN "Region"
                    ELSE '{null}'::int[] END) 

架构：

create table test(id serial, key int,type text,words text[],numbers int[] );

insert into test(key,type,words) select 1,'Name',array['Table'];
insert into test(key,type,numbers) select 1,'product_id',array[2];
insert into test(key,type,numbers) select 1,'price',array[40];
insert into test(key,type,numbers) select 1,'Region',array[23,59];
insert into test(key,type,words) select 2,'Name',array['Table1'];
insert into test(key,type,numbers) select 2,'product_id',array[1];
insert into test(key,type,numbers) select 2,'price',array[34];
insert into test(key,type,numbers) select 2,'Region',array[23,59,61];
insert into test(key,type,words) select 3,'Name',array['Chair'];
insert into test(key,type,numbers) select 3,'product_id',array[5];

select key,"Name",product_id,price,unnest(CASE WHEN array_length("Region", 1) >= 1
               THEN "Region"
               ELSE '{null}'::int[] END) from 
(
  select key,
  max(array_to_string(words,',')) filter(where type='Name') as "Name",
  cast(max(array_to_string(numbers,',')) filter(where type='product_id') as int)  as  "product_id", 
  cast(max(array_to_string(numbers,',')) filter(where type='price') as int)  as  "price" ,
  max(numbers) filter(where type='Region') as "Region"
  from test group by key
)t order by key

key	Name	product_id	price	unnest
1	Table	2	40	23
1	Table	2	40	59
2	Table1	1	34	23
2	Table1	1	34	59
2	Table1	1	34	61
3	Chair	5	null	null

db小提琴here

Answer 2

非常奇怪的数据库设计......我假设你继承了它？

如果没有其他数组值的基数 > 1，那么您可以简单地unnest：

select
  key,
  (max (words) filter (where type = 'Name'))[1] as name,
  (max (numbers) filter (where type = 'product_id'))[1] as product_id,
  (max (numbers) filter (where type = 'price'))[1] as price,
  unnest (max (numbers) filter (where type = 'Region')) as region
from test
group by key

如果它们可以有多个值，那也可以处理。

-- 编辑 2021 年 3 月 15 日--

短版：unnest 反对 null 不会产生一行，因此如果您将 null 值合并到一个包含单个 null 元素的数组中，则应该注意这部分：

select
  key,
  (max (words) filter (where type = 'Name'))[1] as name,
  (max (numbers) filter (where type = 'product_id'))[1] as product_id,
  (max (numbers) filter (where type = 'price'))[1] as price,
  unnest (coalesce (max (numbers) filter (where type = 'Region'), array[null]::integer[])) as region
from test
group by key
order by key

现在对于您没有问的部分...我和至少其他人一直在轻轻地提醒您，您的数据库设计将在每一个转折点都会导致多个问题。它在生产中的事实并不意味着您不应该尽快修复它。

这种设计就是所谓的 EAV - 实体 - 属性 - 值。它有它的用例，但像大多数好东西一样，它也可以在不应该应用的时候应用。想到的用例是，如果您希望用户能够为某些对象动态添加属性。即使那样，也可能有更好/更简单的方法。

举个例子，如果您有一百万个对象，五个属性意味着您必须将其存储为 500 万行，并且大部分空间将用于重复键和属性名称。

只是思考的食物。我们可以继续对您发现的每个新场景进行分类，但最好重做设计。