Auto delete duplicate value in sql

[atuljadhavnetafim]

dear Expert

i am not expert in programming but thanks to all to help me,

i have one table with 5 field in sql table, one of the field having unique values(InvoiceNo), and every month i append this table by using import/export vizard from excel, and that excel having some new value and some old value which is already in sql table, now i want such duplicate value delete automatice at the time of append the table or after that,

currenlty i am doing this in excel, i delete duplicate data in excel and uploade again whole data in sql

please help me

Atul Jadhav