Select 列并且仅在 jsonb 列中 return 满足条件的最后一个元素

Question

我有 table documents，我想要 select 列 foo 和 bar。还有 comments 列，即 jsonb。

但是在comments中我只需要最后一个满足条件的元素"isUser":false.

"select foo, bar, comments from documents 
 where comments @> '[{"isUser":false}]' 
 limit 1 " /*just limit by 1, the latest comment where isUser = false*/

这是 json 在 comments 列中的样子：

[{
    "text": "1 sample lorem ipsum",
    "authorId": "0dcd5a36-2778-4fc4-bbc1-112ed61f1362",
    "timestamp": "2018-11-11T08:46:39.608Z",
    "isUser": false
},{
    "text": "2 sample lorem",
    "authorId": "0dcd5a36-2778-4fc4-bbc1-112ed61f1362",
    "timestamp": "2018-11-11T08:46:41.237Z",
    "isUser": true
},{
...]

对于comments我只需要"isUser":false

中的最后一个对象

Answer 1

您可以使用jsonb_array_elements .. WITH ORDINALITY获取订单

select foo, bar, j.comments
from 
  documents cross 
  join lateral jsonb_array_elements(comments) WITH ORDINALITY j(comments, rn)
WHERE 
  (j.comments ->> 'isUser'):: boolean is false
  ORDER BY j.rn DESC LIMIT 1;

编辑

I want it to limit to 1 json object inside the jsonarray in comments

select DISTINCT ON ( foo, bar) foo,bar,comments
FROM 
( select d.foo,d.bar,j.comments,j.rn
from 
  documents d cross 
    join lateral jsonb_array_elements(comments) WITH ORDINALITY j(comments, rn)
WHERE 
  (j.comments ->> 'isUser'):: boolean is false
  ) s
  ORDER BY foo,bar,rn desc  ;

Demo

Select 列并且仅在 jsonb 列中 return 满足条件的最后一个元素

Select columns and in a jsonb column only return the last element where meets condition

postgresql

postgresql-9.5