get_material_requests_based_on_supplier deduplicated requests with
SELECT DISTINCT (name, transaction_date, company) while ordering by
mr_item.item_code, which is not in the select list. MariaDB allows this;
PostgreSQL rejects it:
psycopg2.errors.InvalidColumnReference: for SELECT DISTINCT,
ORDER BY expressions must appear in select list
so the picker errored out there.
Group by the three selected columns (equivalent to the DISTINCT, so the
same set of requests is returned) and order by Min(item_code). The order
key stays item_code but is now a well-defined aggregate, making the query
valid - and the ordering deterministic and identical - on both engines.
90ef4f4776