Enforce product barcodes to be unique (references #1205)

migrations/0128.sql

@@ -0,0 +1,13 @@
+-- Duplicate product barcodes were most probably not created on purpose,
+-- so just keep the newer one for any duplicates
+DELETE FROM product_barcodes
+WHERE id IN (
+	SELECT MIN(id)
+	FROM product_barcodes
+	GROUP BY barcode
+	HAVING COUNT(*) > 1
+);
+
+CREATE UNIQUE INDEX ix_product_barcodes ON product_barcodes (
+	barcode
+);