Mysql:-
Default password is that there is no password. You can log in to mysql

for example with this command:

mysql -u root



There are also ways to change the password and you will find those

methods from the MySQL manual.



http://www.mysql.com/doc/en/index.html

after doing this command on commane prompt:-
mysql -u root



If this brings you to the 'mysql>' prompt then you can set the password to

anything you like with a couple simple statements:



mysql> use mysql;

mysql> UPDATE user SET Password=Password('newpassword') WHERE User='root';
it will update your password in mysql table user.In mysql there is a database named as Mysql for storing core information

SQL server:-
the service is installed under LocalSystem, with a default "sa" account with a BLANK password!