Here is a quick way to put the contents of a database table into a simple text file. This could be handy if for example, you just want to grab some emails and pop the results into a simple csv file. Your sql statement can be as creative as sql allows. All you are doing here is piping the query to mysql and then saving it to a file.
echo 'select concat(firstname, ', ', lastname, ', ', email) from email_subscribers' \ | mysql -uroot -p emails_database > emails.csv