PostgreSQL - JSON function - postgresql

Question

There's a different format for row_to_json and json_build_object.
For row_to_json the input is:
select ... <table.field> "<json_key"
And for the json_build_object:
"<json_key" , <table.field>
That's surprising to me. Oracle uses similar JSON functions with similar input. This may look like a minor thing, but it makes it harder for me to automate the generation of SELECT statements for complex/nested structures.
Consider this simple example:
CREATE TABLE "users" (
id SERIAL NOT NULL,
name VARCHAR(100),
email_address VARCHAR(150),
PRIMARY KEY(id)
);
INSERT INTO "users" ("id", "name", "email_address")
VALUES (1, 'user1', 'user1#mail.com'), (2, 'user2', 'user2#mail.com');
To fetch the email and the name where email is a dictionary object:
"{""user_name"":""user1"",""email"":{""email_address"" : ""user1#mail.com""}}"
The query would be:
select row_to_json(users) from
(select users.name "user_name" ,
(json_build_object( 'email_address' , users.email_address )) email
from users ) users;
I would like to use the same order of fields in both cases.
The input would be:
<table.field> "<json_key" OR "<json_key" <table.field>
I tried to flip the order using "AS" but it doesn't work:
select row_to_json(users) from
(select users.name "user_name" ,
(json_build_object( users.email_address as 'email_address' )) email
from users ) users;
Maybe with using only row_to_json() or json_build_object()?
Or anything else? (But no left join.)

Answer 1

row_to_json takes an entire row tuple (a record) as input, such as you get it from a subquery. If you don't use those, or don't like row_to_json, don't use it. It's a convenience mainly if you use SELECT * and not want to specify column/field names.
I recommend to use json_build_object with explicit field names, especially if you want to rename them anyway. Your query can and should be written as
SELECT json_build_object(
'user_name', users.name,
'email', json_build_object(
'email_address', users.email_address
)
) AS json_result
FROM users;