-- Drop the unique index on (user_id, shift_date) for work_plan_overrides.
-- MySQL unique indexes don't ignore soft-deleted rows, which would prevent
-- createOverride from soft-deleting an existing override and creating a new
-- one for the same (user_id, shift_date). Application code enforces the
-- "at most one active override per (user_id, shift_date)" invariant.
-- The application-level check is wrapped in a transaction; see
-- src/services/plan.service.ts:createOverride.
--
-- The original index was created in
-- 20260605120000_add_work_plan/migration.sql as `uniq_wpo_user_date`.

-- IMPORTANT ordering: `uniq_wpo_user_date` is the only index covering the
-- `user_id` foreign key, and MySQL refuses to drop an index still needed by a
-- FK. So we CREATE the replacement non-unique index FIRST (giving the FK
-- another covering index), THEN drop the unique one. The reverse order fails
-- with "Cannot drop index ... needed in a foreign key constraint" on a fresh
-- apply.

-- Add a non-unique index for the (user_id, shift_date) lookup used by
-- createOverride's "is there an active override for this user-day?" query
-- and by resolveCell / resolveGrid. This is a plain index, not a unique
-- one — multiple rows (active and soft-deleted) can share the same
-- (user_id, shift_date) pair.
CREATE INDEX `idx_wpo_user_date` ON `work_plan_overrides`(`user_id`, `shift_date`);

DROP INDEX `uniq_wpo_user_date` ON `work_plan_overrides`;
