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-- Migration: add unique constraint on fofo.fofo_order (fofo_id, invoice_number)
-- Paired with idempotent createAndGetFofoOrder() code: concurrent duplicate
-- inserts (client double-clicks, upstream retries) used to deadlock on the
-- idx_invoice_number gap lock — with the unique key, the loser gets a clean
-- DataIntegrityViolationException which the code catches and re-selects.
-- Pre-check on 2026-04-22: zero existing duplicate (fofo_id, invoice_number)
-- groups in the table, so the constraint adds cleanly.
-- Online DDL on InnoDB 5.7+; brief metadata lock only at commit.

ALTER TABLE fofo.fofo_order
  ADD UNIQUE KEY uk_fofo_order_fofo_invoice (fofo_id, invoice_number);

-- Rollback:
-- ALTER TABLE fofo.fofo_order DROP INDEX uk_fofo_order_fofo_invoice;