Question

我正在寻找最佳性能查询来获取关联中不同枚举的计数。

采用以下SQL

CREATE TYPE ITEM_TYPE AS ENUM ('coming', 'new', 'archive');

CREATE TABLE centers
(
  id SERIAL PRIMARY KEY,
  name TEXT NOT NULL,
  created_at timestamp without time zone default (now() at time zone 'utc'),
  updated_at timestamp without time zone default (now() at time zone 'utc')
);

CREATE TABLE items
(
  id SERIAL PRIMARY KEY,
  center_id INT NOT NULL REFERENCES centers(id),
  item_type ITEM_TYPE NOT NULL,
  description TEXT NOT NULL,
  created_at timestamp without time zone default (now() at time zone 'utc'),
  updated_at timestamp without time zone default (now() at time zone 'utc')
);

我想查询所有“中心”，但我也希望根据item_type枚举返回项目计数。

在下面的示例中，ItemNewCount和ItemArchiveCount与枚举相关。

{
    id: 1,
    name: 'Center Name',
    ItemComingCount: 400,
    ItemNewCount: 300,
    ItemArchiveCount: 567
}

Answer 1

只需合并left join, group by and Case运算符

试试这个

SELECT c.id, c.name, 
sum(case when i.item_type = 'coming' then 1 else 0 end) as ItemComingCount,
sum(case when i.item_type = 'new' then 1 else 0 end) as ItemNewCount,
sum(case when i.item_type = 'archive' then 1 else 0 end) as ItemArchiveCount
from centers as c LEFT JOIN items as i ON c.id = i.center_id
group by c.id, c.name

获得最快查询的关联计数

1 个答案: