Implement refund system for sales

refund_migration.sql

@@ -0,0 +1,14 @@
+-- Database Migration Script for Refund System
+-- Run this on existing Petstoredb to add refund functionality
+
+USE Petstoredb;
+
+-- Add refund columns to sale table
+ALTER TABLE sale
+  ADD COLUMN isRefund BOOLEAN DEFAULT FALSE NOT NULL,
+  ADD COLUMN originalSaleId INT NULL,
+  ADD CONSTRAINT fk_original_sale
+    FOREIGN KEY (originalSaleId) REFERENCES sale(saleId);
+
+-- Verify the changes
+DESCRIBE sale;