How to generate JSON array from multiple rows, then return with values of another table - sql

Question

I am trying to build a query which combines rows of one table into a JSON array, I then want that array to be part of the return.
I know how to do a simple query like
SELECT *
FROM public.template
WHERE id=1
And I have worked out how to produce the JSON array that I want
SELECT array_to_json(array_agg(to_json(fields)))
FROM (
SELECT id, name, format, data
FROM public.field
WHERE template_id = 1
) fields
However, I cannot work out how to combine the two, so that the result is a number of fields from public.template with the output of the second query being one of the returned fields.
I am using PostGreSQL 9.6.6
Edit, as requested more information, a definition of field and template tables and a sample of each queries output.
Currently, I have a JSONB row on the template table which I am using to store an array of fields, but I want to move fields to their own table so that I can more easily enforce a schema on them.
Template table contains:
id
name
data
organisation_id
But I would like to remove data and replace it with the field table which contains:
id
name
format
data
template_id
At the moment the output of the first query is:
{
"id": 1,
"name": "Test Template",
"data": [
{
"id": "1",
"data": null,
"name": "Assigned User",
"format": "String"
},
{
"id": "2",
"data": null,
"name": "Office",
"format": "String"
},
{
"id": "3",
"data": null,
"name": "Department",
"format": "String"
}
],
"id_organisation": 1
}
This output is what I would like to recreate using one query and both tables. The second query outputs this, but I do not know how to merge it into a single query:
[{
"id": 1,
"name": "Assigned User",
"format": "String",
"data": null
},{
"id": 2,
"name": "Office",
"format": "String",
"data": null
},{
"id": 3,
"name": "Department",
"format": "String",
"data": null
}]

Answer 1

The feature you're looking for is json concatenation. You can do that by using the operator ||. It's available since PostgreSQL 9.5
SELECT to_jsonb(template.*) || jsonb_build_object('data', (SELECT to_jsonb(field) WHERE template_id = templates.id)) FROM template

Answer 2

Sorry for poorly phrasing what I was trying to achieve, after hours of Googling I have worked it out and it was a lot more simple than I thought in my ignorance.
SELECT id, name, data
FROM public.template, (
SELECT array_to_json(array_agg(to_json(fields)))
FROM (
SELECT id, name, format, data
FROM public.field
WHERE template_id = 1
) fields
) as data
WHERE id = 1
I wanted the result of the subquery to be a column in the ouput rather than compiling the entire output table as a JSON.