Prevent duplication record in table

Hi All,

Need your guys help, let say I wanted to insert a record to a table name “Inventory”, with following column (please see below), then have done the mysql mapping.

How do I know if what I have inserted is a duplicate as there is no notification saying the record entry is duplication (as duplication will no go through the database). Is there an example, where we can do it in Javascript using form maker? or other method?

Inventory
`txtBarcode UNIQUE ,
txtItemDescription ,
txtCategory,
txtStockOrigin,
iCurrentQuantity,
dLastPrice.

Thanks in advance