3.11使用大學模式，用SQL寫出如下查詢。

a.找出所有至少選修了一門Comp. Sci. 課程的學生姓名，保證結果中沒有重複的姓名。

with target_course(id, title) as (
	select course_id, title from course where dept_name = 'Comp. Sci.'
)
select distinct name from takes natural join student
where course_id in (select id from target_course);

   name   
----------
 Bourikas
 Zhang
 Shankar
 Williams
 Levy
 Brown
(6 rows)
 

b.找出所有沒有選修在2009年春季之前開設的任何課程的學生的ID和姓名。

with student_id(ID) as (
(select ID from student)
except -- 減去所有選修2009年春季課程的學生
--找出所有選修2009年春季開設課程的學生
(select distinct ID from takes where (course_id, sec_id, semester, year) 
 in(
--找出2009年春季開設的所有課程
select course_id, sec_id, semester, year from section where year = 2009 and semester = 'Spring'
 )))
select ID, name from student natural join student_id order by ID;
 

  id   |   name   
-------+----------
 00128 | Zhang
 19991 | Brandt
 23121 | Chavez
 44553 | Peltier
 45678 | Levy
 55739 | Sanchez
 70557 | Snow
 76543 | Brown
 98765 | Bourikas
 98988 | Tanaka
(10 rows)

c.找出每個系教師的最高工資值。可以假設每個系至少有一位教師。

select dept_name, max(salary) from instructor
group by dept_name;
 

 dept_name  |    max    
------------+-----------
 Finance    |  90000.00
 History    |  62000.00
 Physics    |  95000.00
 Music      |  40000.00
 Comp. Sci. | 101200.00
 Biology    |  72000.00
 Elec. Eng. |  80000.00
(7 rows)

d.從前述查詢所計算出的每個系最高工資中選出最低值。

with dept_salary_max(dept_name, salary) as (
	select dept_name, max(salary) from instructor
	group by dept_name
) select min(salary) from dept_salary_max;

   min    
----------
 40000.00
(1 row)