volgens Colin Fraser.
Part of the backup process is to compress data. The .sql file is actually a text file that you can use to restore your database as it was when the file was created, very handy too. Thinks like images and other files stored in the moodledata folder are not included in the .sql file but the paths to them are. The table structure in the database takes up a lot more room than it does in the .sql file, it is only a line of text for each field in the file. So no it is not an issue.
To restore the .sql file, open something like phpMyAdmin and upload the file, and see what phpMyAdmin can do with it.