It is quite easy to install MySQL on FreeBSD using packages. I normally like to install from source but packages are so simple and quick to upgrade it is useful to use them if you don’t require any special make options. This is the following commands I use to install MySQL with all the appropriate things done for it to run nicely.
pkg_add -r mysql51-server
Add the following line
chown -R mysql /var/db/mysql/
chgrp -R mysql /var/db/mysql/
cp /usr/local/share/mysql/my-medium.cnf /etc/my.cnf
/usr/local/bin/mysqld_safe -user=mysql &
/usr/local/bin/mysqladmin -u root password newpassword