How are you populating data is Salesforce? if you are making bulk inserts in Salesforce, use the import wizard to enter data which doesn't have duplicates: http://help.salesforce.com/apex/HTViewSolution?urlname=Will-the-import-wizard-prevent-duplicate-records-1327109138176&language=en_US
http://help.salesforce.com/apex/HTViewSolution?urlname=Will-the-import-wizard-prevent-duplicate-records-1327109138176&language=en_US