-- Add missing customer_ref column
ALTER TABLE purchase_orders ADD COLUMN IF NOT EXISTS customer_ref VARCHAR(255);

-- Update status check constraint to include 'shipped'
ALTER TABLE purchase_orders DROP CONSTRAINT IF EXISTS purchase_orders_status_check;
ALTER TABLE purchase_orders ADD CONSTRAINT purchase_orders_status_check
  CHECK (status IN ('draft', 'confirmed', 'in_production', 'shipped', 'completed', 'cancelled'));