The correct statement to restore a database from a file and clean the data is: psql -d mydatabase < filename.sql. So, the correct option is: D) psql -d mydatabase <
To clean and restore a PostgreSQL database named "mydatabase" from a file, you would use the following command: `psql -d mydatabase < filename.sql`.
This command leverages the `psql` utility, specifying the target database with the `-d` flag, and then using the input redirection (`<`) to read SQL commands from the specified file (`filename.sql`). This process helps in cleaning and populating the database with the data and schema defined in the SQL file. The other options mentioned (A, B, C) do not accurately represent the standard syntax for restoring a database from a file in PostgreSQL.
Option D is the answer.