How to stop array_to_json from interpolating column names that weren't there

Guyren Howe <guyren@xxxxxxxxx> · Wed, 19 Jul 2017 19:30:18 -0700

9.6
I’ve a view that shows information about schemas:
 SELECT schemata.catalog_name,
    schemata.schema_name,
    ('/'::text || (schemata.schema_name)::text) AS schema_name_address
   FROM information_schema.schemata
  ORDER BY schemata.catalog_name, schemata.schema_name

Fine. I now want to turn that result set into a JSON array. I can do this:

		SELECT
			ARRAY_AGG(foo) AS foos
		FROM (
			SELECT
				row_to_json(schemata_)
			FROM
				schemata_)
			AS
				foo
and I get this:

{“(\”{\"\"catalog_name\"\":\"\"ds2_development\"\",\"\"schema_name\"\":\"\"admin\"\",\"\"schema_name_address\"\":\"\"/admin\"\"}\")","(\"
…

which is great. I have an array of perfect JSON objects. Now I just need to turn that into a single JSON object. But when I do the obvious:

SELECT array_to_json(
		SELECT
			ARRAY_AGG(foo) AS foos
		FROM (
			SELECT
				row_to_json(schemata_)
			FROM
				schemata_)
			AS
				foo
)

I get a syntax error. And when I do:

SELECT TO_JSON(foos) FROM (
		SELECT
			ARRAY_AGG(foo) AS foos
		FROM (
			SELECT
				row_to_json(schemata_)
			FROM
				schemata_)
			AS
				foo
) AS bar

Postgres tries to be helpful by interpolating a column name I don’t want (here, row_to_json):

[{“row_to_json":{"catalog_name":"ds2_development","schema_name":"admin","schema_name_address":"/admin"}},{"row_to_json":{"catalog_name":"ds2_development","schema_name":"anon","schema_name_address":"/anon"}},{"row_to_json":
…

I could fix this in PLV8 a tad inefficiently, but I feel like I ought to be able to do this in pure SQL and there’s some heuristic or Yet Another Weird Corner Case I’m as yet unaware of.

So: can I do this in SQL? How?