查询包含JSON对象数组的jsonb列

Question

我使用PostgreSQL 9.5和Rails 5.我想查询jsonb下面显示的包含JSON对象数组的列,以返回包含的所有JSON数组元素{"kind":"person"}并执行计数.我使用
的SQL显示在json数据下面.运行查询只返回一个空数组.

我已经尝试了这里和这里建议的查询.

这就是我的jsonb数据:

   '[
        {"kind":"person", "filter_term":"56","selected_attr":"customer"},
        {"kind":"email", "filter_term":"marketer","selected_attr":"job_title"}
      ]'

我想要一个sql查询返回:

                             data
----------------------------------------------------------------------
 '{"kind":"person", "filter_term":"56","selected_attr":"customer"}'
(1 row)

和另一个返回数组的查询,以便我可以在我的应用程序中调用count并在其上循环以创建表单:

 data
----------------------------------------------------------------------
 '[{"kind":"person", "filter_term":"56","selected_attr":"customer"}]'
 (1 row)

我试过这个SQL查询:

 "SELECT * FROM \"segments\" WHERE (payload @> '[{\"kind\":\"person\"}]')"

我也试过这个查询:

  "SELECT payload FROM segments WHERE payload @> '[{\"kind\":\"person\"}]'::jsonb;"

这是第三个查询:

 "SELECT * FROM segments s WHERE s.payload->'\"#{a}\"' @> '[{\"kind\":\"person\"}]';"

该模型:

class Segment < ApplicationRecord
 store_accessor :payload,:kind, :filter_term, :selected_model_name, :selected_attr, :limit, :selected_operator
end

迁移:

create_table "segments", force: :cascade do |t|

  t.jsonb    "payload",    default: "[]", null: false
  t.index ["payload"], name: "index_segments_on_payload", using: :gin

end

Answer 1

假设这个表定义:

CREATE TABLE segments (segments_id serial PRIMARY KEY, payload jsonb);

使用这样的JSON值:

INSERT INTO segments (payload)
VALUES ('[
            {
                "kind": "person",
                "limit": "1",
                "filter_term": "56",
                "selected_attr": "customer",
                "selected_operator": "less_than"
            },
            {
                "kind": "email",
                "filter_term": "marketer",
                "selected_attr": "job_title",
                "selected_operator": "equals"
            }
        ]'
   );

• 您希望返回包含键/值对"kind":"person"(不是嵌套的JSON对象{"kind":"person"})的JSON 数组的元素 - 并计算数组元素和表行(每行可能有多个匹配的数组元素).

解决方案

要获取列中包含限定jsonb值的行数segments:

SELECT count(*)
FROM   segments s
WHERE  s.payload @> '[{"kind":"person"}]';

获取所有符合条件的JSON数组元素(本身就是JSON对象) - 加上元素的总数(可能同时大于上面的数量:

SELECT j.*
FROM   segments s
JOIN   LATERAL jsonb_array_elements(s.payload) j(elem) ON j.elem @> '{"kind":"person"}'
WHERE  s.payload @> '[{"kind":"person"}]';

返回:

elem
------------------------------------------------------------
{"kind": "person", "limit": "1", "filter_term": "56", ... }

为了得到所有:

SELECT j.*, count(*) OVER () AS ct_elem, s.ct_rows
FROM  (
   SELECT payload, count(*) OVER () AS ct_rows
   FROM   segments
   WHERE  payload @> '[{"kind":"person"}]'
   ) s
JOIN   LATERAL jsonb_array_elements(s.payload) j(elem) ON j.elem @> '{"kind":"person"}';

返回(对于包含更多条目的表):

elem                      | ct_elem | ct_rows
--------------------------+---------+---------
{"kind": "person",  ... } | 4       | 3
{"kind": "person",  ... } | 4       | 3
...

但我认为你真的想要这个:

SELECT a.*
     , sum(ct_elem_row) OVER () AS ct_elem_total
     , count(*)         OVER () AS ct_rows
FROM   segments s
JOIN   LATERAL (
   SELECT json_agg(j.elem) AS filtered_payload, count(*) AS ct_elem_row
   FROM   jsonb_array_elements(s.payload) j(elem)
   WHERE  j.elem @> '{"kind":"person"}'
   ) a ON ct_elem_row > 0
WHERE  s.payload @> '[{"kind":"person"}]';

返回(对于包含更多条目的表):

filtered_payload                                     | ct_elem_row | ct_elem_total | ct_rows
-----------------------------------------------------+-------------+---------------+---------
[{"kind": "person", ... }]                           | 1           | 4             | 3
[{"kind": "person", ... }]                           | 1           | 4             | 3
[{"kind": "person", ... }, {"kind": "person", ... }] | 2           | 4             | 3

这标识匹配的行,然后选择匹配的数组元素,并且每行只构建一个数组.加上重要.

为获得最佳性能,您将拥有如下jsonb_path_opsGIN索引:

CREATE INDEX segments_path_ops_gin_idx ON segments 
USING  gin (payload jsonb_path_ops);

(但是,提供更多不同查询的更通用的索引可能是更好的选择.)

有关:

• 用于在JSON数组中查找元素的索引

• 查询JSON类型中的数组元素

• 在应用LIMIT之前获得结果计数的最佳方法

术语

我们正在处理一个包含 JSON数组的JSON对象,保存为Postgres jsonb数据类型 - 简称为"JSON数组",但不是 "JSON数组".