json_agg() with pseudo row - json

Question

CREATE TABLE content
(
code INTEGER NOT NULL
, nameid TEXT NOT NULL
)
INSERT INTO content(code, nameid) VALUES
( 0, 'Support')
, ( 1, 'Adrenaline')
, ( 2, 'Aquapark')
;
Need select all content as JSON array-object named 'content' with pseudo row with code = '' and nameid = 'All'
What i did:
1) Simple select
SELECT
json_build_object('content', (SELECT json_agg(json_build_object(
'code', s.code::TEXT
, 'nameid', s.nameid::TEXT
))
FROM content s
)
);
Result is
{
"content": [{
"code": "0",
"nameid": "Support"
},
{
"code": "1",
"nameid": "Adrenaline"
},
{
"code": "2",
"nameid": "Aquapark"
}
]
}
All fine, but how to add pseudo row?
2) Best i can did
SELECT
json_build_object('content', json_build_array(
json_build_object(
'code', ''
, 'nameid', 'All'::TEXT),
(SELECT json_agg(json_build_object(
'code', s.code::TEXT
, 'nameid', s.nameid::TEXT
))
FROM content s
))
);
Result is
{
"content": [{
"code": "",
"nameid": "All"
},
[{
"code": "0",
"nameid": "Support"
},
{
"code": "1",
"nameid": "Adrenaline"
},
{
"code": "2",
"nameid": "Aquapark"
}
]
]
}
And we have array in array, as in sql as in json, but i can not understand how to combine json_agg with pseudo row.

Answer 1

Use to_json() and union all:
select jsonb_build_object('content', json_agg(to_json))
from (
select to_json(c)
from (select '' as code, 'All' as nameid) c
union all
select to_json(c)
from content c
) s
Output:
{
"content": [
{
"code": "",
"nameid": "All"
},
{
"code": 0,
"nameid": "Support"
},
{
"code": 1,
"nameid": "Adrenaline"
},
{
"code": 2,
"nameid": "Aquapark"
}
]
}
The version with an alias in the derived table:
select jsonb_build_object('content', json_agg(codes))
from (
select to_json(c) as codes
from (select '' as code, 'All' as nameid) c
union all
select to_json(c)
from content c
) s