When migrating from Voyager to Alma, duplicate (in other words, non-unique) item barcodes will be changed to "-". This may not be desirable and you may want to fix them before migration.
This query, which you can run in Voyager's Prepackaged Access Reports, should help you to identify duplicate barcodes in your database and fix them.
SELECT ITEM_BARCODE.ITEM_BARCODE, Count(ITEM_BARCODE.ITEM_ID) AS CountOfITEM_ID
GROUP BY ITEM_BARCODE.ITEM_BARCODE
For other queries that may be useful, see my "Surviving Almanado: tips for a successful pre-implementation" presentation's Accompanying Materials.
If you need assistance in running custom SQL queries in Prepackaged Access Reports, consult the Voyager Customer Listserv.