如何在PostgreSQL中根据字段排序获取从第二高到最低的值记录

Question

这里我有一个 JSON 字段，我想 select 每个 id 上从高到低的第二个记录数据是

JSON 看起来像这样

{
    "user": [
        {
            "user_name": "Devang",
            "user_weight": 0.7676846955248864
        },
        {
            "user_name": "Meet",
            "user_weight": 1.1021
        },
        {
            "user_name": "Devang",
            "user_weight": 0.16163873153859706
        },
        {
            "user_name": "Rajan",
            "user_weight": 0.22163873153859706
        }
    ],
    "address": [
        {
            "address_name": "India"
        }
    ]
}

我执行的查询是

WITH cte AS (
SELECT id, ('{user,'||index-1||'}')::text[] as json_path, value->'user_weight'
FROM user_table, jsonb_array_elements(json_field->'user')
WITH ordinality arr(value, index) WHERE arr.value->>'user_name' IN ('Devang', 'Meet') order by id, value->'user_weight' DESC
) select * from cte;

获得这种记录

id  json_path   ?column?
1   {user,1}    1.1021
1   {user,0}    0.7676846955248864
1   {user,2}    0.16163873153859706
2   {user,0}    0.7676846955248864
2   {user,1}    0.07447325861051013

我想要这样的从高到低的第二个记录

id  json_path   ?column?
1   {user,1}    1.1021 # this is the highest one in 1 id so I do not need this
1   {user,0}    0.7676846955248864
1   {user,2}    0.16163873153859706
2   {user,0}    0.7676846955248864   # this is the highest one in 2 ids so. I do not want
2   {user,1}    0.07447325861051013

输出将是

id  json_path   ?column?
1   {user,0}    0.7676846955248864
1   {user,2}    0.16163873153859706
2   {user,1}    0.07447325861051013

看这里Demo

任何答案将不胜感激

Answer 1

有很多方法可以做到这一点，但如果您想玩 window 函数，您可以 RANK() 或 DENSE_RANK() 通过 id 的权重并消除第一行外部查询：

WITH cte AS (
  SELECT id, ('{user,'||index-1||'}')::text[] as json_path, (value->'user_weight')::text::numeric AS weight
  FROM user_table, jsonb_array_elements(json_field->'user')
  WITH ordinality arr(value, index) 
  WHERE arr.value->>'user_name' IN ('Devang', 'Meet') 
  ORDER BY id, value->'user_weight' DESC
) 
SELECT * FROM (
  SELECT cte.*, 
    RANK() OVER (PARTITION BY id ORDER BY id,weight DESC
                 RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS r
  FROM cte) j
WHERE r > 1;

演示：db<>fiddle

Answer 2

使用 window 函数和分区，我们可以像这样抓取并消除第一行：

WITH cte AS (
   SELECT id, ('{user,'||index-1||'}')::text[] as json_path, value->'user_weight', ROW_NUMBER() OVER(PARTITION BY id order by value->'user_weight' DESC ) as row_num
   FROM user_table, jsonb_array_elements(json_field->'user')
    WITH ordinality arr(value, index) WHERE arr.value->>'user_name' IN ('Devang', 'Meet') order by id, value->'user_weight' DESC
) 
select * from cte where row_num>1;

这里Demo

如何在PostgreSQL中根据字段排序获取从第二高到最低的值记录

How to get the second highest to lowest value record on the based on order by field in PostgreSQL

sql

postgresql

common-table-expression

jsonb