-- =============================================
-- MIGRATION: Fix Customer Order FK + Order Merging
-- =============================================
-- Problem: orders.user_id has FK to users(id) but customer QR orders use user_id=0
-- which doesn't exist, causing FK violation.
-- Solution: Make user_id nullable so customer orders can use NULL.

-- Step 1: Make user_id nullable in orders table
ALTER TABLE orders MODIFY COLUMN user_id INT NULL;

-- Step 2: Fix any existing orders that have user_id=0 (invalid FK)
UPDATE orders SET user_id = NULL WHERE user_id = 0;