Try:

mysql -u username -p database_name < file.sql

Check MySQL Options.

Note-1: It is better to use the full path of the SQL file file.sql.

Note-2: Use -R and --triggers to keep the routines and triggers of original database. They are not copied by default.

Note-3 You may have to create the (empty) database from mysql if it doesn't exist already and the exported SQL don't contain CREATE DATABASE (exported with --no-create-db or -n option), before you can import it.