来自Postgres API的嵌套JSON，架构不存在？

Question

I have a SQL API to my Postgres database that returns JSON.

I have two tables: holidays , which has a schema of name , hd_id . And photos , which are photos take on that day. Its schema is url , caption , h_id .

I'd like to create a nested json object like the one down below. The SQL I'm running is

    SELECT holidays.name, holidays.h_id, 
    concat('[', group_concat(concat('{"src":"', photos.url, '","caption":"', photos.caption '"}', separater ','), ']') ) 
    FROM holidays 
    INNER JOIN photos 
    ON holidays.h_id = photos.h_id 
    GROUP BY holidays.h_id

But that gives me the error "schema "photos" does not exist" . Photos is a table, not a schema. I don't seem to be making the same mistake as this seemingly related question . I'm not sure how else to structure the JOIN.

Here's the desired JSON output.

   [
    {
        name: 'Labor Day',
        h_id: 'a1',
        photos: [
            {
                src: 'url',
                caption: 'text'
            },
            {
                src: 'url',
                caption: 'text'
            }
        ]
    },
    {
        name: 'MLK Day',
        h_id: 'a2',
        photos: [
            {
                src: 'url',
                caption: 'text'
            },
            {
                src: 'url',
                caption: 'text'
            }
        ]
    }
   ]

Answer 1

There's no group_concat in PostgreSQL . You may use string_agg :

select
    h.name, h.h_id, 
    '[' || string_agg('{"src":"' || p.url || '", "caption":"' || p.caption  || '"}', ',') || ']'
from holidays as h
    inner join photos as p on h.h_id = p.h_id 
group by h.name, h.h_id

see sql fiddle demo with this example

Or use JSON functions . There's also nice JSON support in version 9.3