如何在 Postgres 的 json_build_object() 中进行 GROUP BY 和 COUNT

Question

我想在 table（或 CTE）上执行多个 GROUP BY 和 COUNT 操作，并将输出作为单个 JSON.

考虑 Postgres 数据库中的以下 table：

Name	Author	Publisher	Language
Book1	Jason	Penguin	English
Book2	Jason	Macmillan	English
Book3	Paul	Macmillan	English
Book4	Julia	Macmillan	English
Book5	Julia	Penguin	English

这是我当前的 SQL 查询

WITH first_selection AS (
    SELECT *
    FROM books
    where language='English')
SELECT json_build_object('author_options', json_agg(DISTINCT(author)),
                         'publisher_options', json_agg(DISTINCT(publisher)))
FROM first_selection

为此我得到了这个输出：

{
    "author_options":["Jason","Paul","Julia"],
    "publisher_options":["Penguin,"Macmillan"]
}

问题是我还需要每个出版商的图书数量，但我一直收到错误消息，指出不允许嵌套聚合。

我需要 JSON 输出中的图书数量。不一定在任何特定结构中，但信息需要存在。基本上我想要一个看起来像这样的输出：

{
    "author_options":["Jason","Paul","Julia"],
    "publisher_options":["Penguin,"Macmillan"],
    "publisher_details": {
                             "Penguin": 2,
                             "Macmillan": 3
                          }
}

如何计算每个出版商的图书数量并将结果放入 JSON？

Answer 1

 create table books (Name varchar(50), Author varchar(50), Publisher varchar(50), Language varchar(50));
 
 insert into books values('Book1',  'Jason',    'Penguin',      'English');
 insert into books values('Book2',  'Jason',    'Macmillan',    'English');
 insert into books values('Book3',  'Paul',     'Macmillan',    'English');
 insert into books values('Book4',  'Julia',    'Macmillan',    'English');
 insert into books values('Book5',  'Julia',    'Penguin',      'English');

查询：

 WITH first_selection AS (
     SELECT *
     FROM books
     where language='English')
 , publisherscount as
 (
 select Publisher, count(*) pcount
 from books
 group by publisher
 )
 SELECT json_build_object('author_options', json_agg(DISTINCT author),
                          'publisher_options', json_agg(DISTINCT publisher),
                          'publisher_details',(select   array_to_json(array_agg(json_build_object(publisher,pcount)))
                          from publisherscount)
                         )
 FROM first_selection

输出：

json_build_object
{author_options : [Jason, Julia, Paul], publisher_options : [Macmillan, Penguin], publisher_details : [{Macmillan : 3},{Penguin : 2}]}

dbhere

Answer 2

您可以在单独的步骤中汇总发布商，然后将其包含在最终结果中：

with first_selection as (
  select *
  from books
  where language = 'English'
), pub_info as (
  select json_object_agg(publisher, cnt) as details
  from (
    select publisher, count(*) as cnt
    from first_selection
    group by publisher
  ) t
)
SELECT json_build_object('author_options', json_agg(distinct author),
                         'publisher_options', json_agg(distinct publisher),
                         'publisher_details', (select details from pub_info))
FROM first_selection

Online example

如何在 Postgres 的 json_build_object() 中进行 GROUP BY 和 COUNT

How to do a GROUP BY and COUNT within json_build_object() in Postgres

sql

postgresql

json

common-table-expression