Invoice Error

The endpoint “https://default-dot-unicommerce-integration-prod.appspot.com/_ah/api/esb/v1/orders/processing” receives a request to Get the URL of the invoice stored on the google cloud storage.
Our approach was to first check if the invoice is present in DB or not for the requested “customerOrderNumber”. If not present then only we generate it from unicommerce else return the URL present in DB. We assumed that for each customerOrderNumber we will have only one shipment present in shipments table in DB.
Earlier we were using the query
SELECT shipments.id, shipments.invoice_url, shipments.externalShipmentID FROM orders LEFT JOIN order_items ON order_items.order_id = orders.id LEFT JOIN shipments ON order_items.shipment_id = shipments.id WHERE orders.customerOrderNumber=:customerOrderNumber AND order_items.status = 'CREATED'
The issue was because there were multiple shipments present for an customerOrderNumber, we were getting an SQL exception. So we changed our DB query
SELECT shipments.id, shipments.invoice_url, shipments.externalShipmentID FROM orders LEFT JOIN order_items ON order_items.order_id = orders.id LEFT JOIN shipments ON order_items.shipment_id = shipments.id WHERE orders.customerOrderNumber=:customerOrderNumber AND order_items.status = 'CREATED' GROUP BY shipments.id