Question

如何对使用json聚合的子查询的结果进行排序？

如果我有这样的架构：

my-classes-1.0.1.jar

我通过子查询在json列上聚合plan_items结果。像这样：

CREATE TABLE plans( id integer NOT NULL, name character varying(255));
CREATE TABLE plan_items ( id integer NOT NULL, plan_id integer NOT NULL, expected_at date, status integer);

JSON聚合按预期工作，并提供我需要的结果。好。但我无法订购结果。

我试过了：

SELECT
  plans.id,
  plans.name,
  jsonb_agg((SELECT pi_cols FROM 
       (SELECT plan_items.id, plan_items.expected_at, plan_items.status) pi_cols
      )) AS plan_items_data
FROM
  plans
  INNER JOIN plan_items ON plan_items.plan_id = plans.id
GROUP BY
  plans.id,
  plans.name
ORDER BY plans.id;

还有：

  jsonb_agg((SELECT pi_cols FROM 
       (SELECT plan_items.id, plan_items.expected_at, plan_items.status ORDER BY plan_items.expected_at) pi_cols
      )) AS plan_items_data

但这些都没有解决。

有什么想法吗？

Answer 1

根据Abelisto的建议，只需使用简单的aggregate expression with ordering：

jsonb_agg(plan_items ORDER BY plan_items.expected_at) AS plan_items_data

Answer 2

使用所需的排序顺序连接表，并使用横向连接选择jsonb_agg()的列：

select s.plan_id id, name, jsonb_agg(pi_col)
from (
    select p.id plan_id, p.name, pi.id, expected_at, status
    from plans p
    join plan_items pi 
    on p.id = pi.plan_id
    order by p.id, expected_at
    ) s,
lateral (
    select plan_id id, expected_at, status
    ) pi_col
group by 1, 2
order by 1;

上述查询似乎比选择列表中具有子查询的查询更自然，更灵活（在大多数情况下更快）。但是为了获得更好的性能，您还应该使用Abelisto的建议：

select s.plan_id id, name, json_agg(pi_col order by pi_col.expected_at)
from (
    select p.id plan_id, p.name, pi.id, expected_at, status
    from plans p
    join plan_items pi 
    on p.id = pi.plan_id
    ) s,
lateral (
    select plan_id id, expected_at, status
    ) pi_col
group by 1, 2
order by 1;

Postgresql jsonb_agg子查询排序

2 个答案: