Example:
Student
studentId
name
Staff
staffId
name
Account
accountId
foreignKeyId(studentId or staffId)
username
password
usertype
Example:
studentId
name
staffId
name
accountId
foreignKeyId(studentId or staffId)
username
password
usertype
IMHO strange design choice. You better go all the way around:
Account
-------
accountid
username
password
usertype
...
Student
-------
studentid
accountid
name
...
Staff
-----
staffid
accountid
name
...
Both tables should be InnoDB. InnoDB details - http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html
The following Stack Overflow answer could help.