Find the name of Physicians who are affiliate with surgery or Psychiatry department.
select t1.name from physician as t1 join affiliated_with as t2 on t1.employeeid = t2.physician join department as t3 on t2.department = t3.departmentid where t3.name = 'Surgery' or t3.name = 'Psychiatry'
Sorry for my mistake. 
What is the Physician name of the following Employee ID 2? tell me the SSN.
select name,ssn from physician where employeeid = 2
yes
select name,ssn,employeeid from physician where position = "Staff Internist"
which department has most number of head? tell me department ID,
select departmentid from department order by head desc limit 1
which department has least number of head? tell me department ID,And department name?
select departmentid,name from department order by head limit 1