Replacing data

Hi

 

I want to replace all the data in a database with an earlier backup I took.  I have a plain sql-script dump (backup.sql) and am using the following command to replace the current data:

 

psql -U postgres dbname < backup.sql

 

However, the command seems to append the data to the database so that I have the old data and any new data added since the backup was taken.  How can I replace all the data so that my database only contains data from the backup?  Maybe I'm using the wrong backup and restore method?

 

Thanks