PostgreSQL error code

PostgreSQL error 22030

22030 is the SQLSTATE PostgreSQL reports for duplicate json object key value, in class 22, Data Exception.

SQLSTATE	22030
Condition name	duplicate_json_object_key_value
Class	22 — Data Exception

Reproduce it, then fix it

Several products share a category, and json_object_agg_unique refuses repeated keys. Group first so each key appears once, with the values collected into an array. Run the broken query to see the error, then switch to the fixed one. Edit either freely; every run is rolled back.

SELECT json_object_agg_unique(category, name) FROM products;

SELECT json_object_agg(category, names)
FROM (
  SELECT category, json_agg(name) AS names
  FROM products
  GROUP BY category
) AS c;

Source: PostgreSQL documentation, Appendix A