insert new record with not duplicate record

i want to insert new record which is will not duplicate with the previous record.
if the record duplicate, the error message will appear.how can i do it??

Unless you have your database fields setup with a UNIQUE flag then you can do a select first and check against it.

e.g.

username = "john"

SELECT from table where field = username

if NOT rs.EOF then
error - name already exists
else
INSERT INTO field values (username)