- Replace MySQL-only `ifnull(...)` with `coalesce(...)` in the two
source/second-source percentage subqueries that remain raw (they
interpolate dynamic table/field names).
- zero_amount_refdocs: raw `sql_list` → `frappe.get_all(pluck="name")`.
- update_billing_status: two raw `ifnull(sum(qty), 0)` selects → frappe.qb
`Sum`; an empty result yields None and flt(None) == 0, matching the old
ifnull behaviour.
Behaviour is unchanged on MariaDB. The percentage path (coalesce subquery)
is exercised by test_selling_controller's Sales Order -> Delivery Note
per_delivered test on both engines.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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