It works with SQLite too - the functions have different names (json_group_array() and json_object() rather than PostgreSQL's json_agg() and json_build_object()) but they work pretty much exactly the same.

The one JSON PostgeSQL feature that SQLite doesn't have yet and I miss is row_to_json(record) which serializes an entire row without you needing to specifically list the column names.

I've not tried this stuff in MySQL myself yet but it looks like JSON_ARRAYAGG() might be the equivalent there: https://dev.mysql.com/doc/refman/8.4/en/aggregate-functions....