Ordering json structure using json_build_object and json_build_array in Postgresql

Question

I am trying to recreate this json using json_build_object and json_build_array in postgresql

Here is my desired output:

[
  {
    "name": "Albert",
    "Gender": "Male",
    "tags": [
      "Student",
      "Geography"
    ]
  }
]

Here is my query:

SELECT 

json_build_array(json_build_object(

    'tags',jsonb_build_array('Student','Geography'),

     'Gender','Male',

    'name', 'name'

)) 

FROM student_list

But when I run this query I get the Gender part appearing first and not like my desired output.

Here is the output I get after running my query

[
  {
    "Gender": "Male",
    "name": "Albert",
    "tags": [
      "Student",
      "Geography"
    ]
  }
]

What can I do to get it like my desired output and why is not following the order in my query. I tried to rearrange the statements in the query but I noticed that the Gender always will pop first and not like my desired output.

Can someone tell me what I am doing wrong.

Vao Tsun · Accepted Answer · 2018-01-12 08:55:56Z

https://www.json.org/

An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace). Each name is followed by : (colon) and the name/value pairs are separated by , (comma).

so you can't expect order in object - only in array

of course you can always treat json as text and order it with some awful clutch, like having {"b":1,"c":4,"a":"foo"}:

t=# with c(j) as (values('{"b":1,"c":4,"a":"foo"}'::json))
, p as (select json_object_keys(j) k, j->json_object_keys(j) v from c)
, r as (select '{'||string_agg('"'||k||'":'||v,',') over (order by k desc) ||'}' jsn from p)
select jsn from r order by length(jsn) desc limit 1;
           jsn
-------------------------
 {"c":4,"b":1,"a":"foo"}
(1 row)

ordered descending and :

t=# with c(j) as (values('{"b":1,"c":4,"a":"foo"}'::json))
, p as (select json_object_keys(j) k, j->json_object_keys(j) v from c)
, r as (select '{'||string_agg('"'||k||'":'||v,',') over (order by k asc) ||'}' jsn from p)
select jsn from r order by length(jsn) desc limit 1;
           jsn
-------------------------
 {"a":"foo","b":1,"c":4}
(1 row)

ascending...

but as soon as you cast it to json, the order in object looses sence...

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