[Assignment 1 - DB] Nguyen Le Thien An

sol-1.sql

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+-- Leetcode Problems
+
+-- https://leetcode.com/problems/capital-gainloss/description/
+select stock_name, sum(case when operation = "Buy" then -price
+                            else +price end) 
+                    as capital_gain_loss
+from Stocks
+group by stock_name;
+
+-- https://leetcode.com/problems/count-salary-categories/description/
+select t.category, count(a.category) as accounts_count
+from (
+  select 'Low Salary' as category
+  union
+  select 'Average Salary' as category
+  union
+  select 'High Salary' as category
+) as t
+left outer join (
+  select case when income < 20000 then 'Low Salary'
+              when income > 50000 then 'High Salary'
+              else 'Average Salary' end as category
+  from Accounts
+) as a on a.category = t.category
+group by t.category;
+

sol-2.sql

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+create database be05;
+
+create table be05.professor(
+	prof_id int not null,
+    prof_lname varchar(50),
+    prof_fname varchar(50),
+    primary key (prof_id)
+);
+
+create table be05.student(
+	stud_id int not null,
+    stud_fname varchar(50),
+    stud_lname varchar(50),
+    stud_street varchar(255),
+    stud_city varchar(50),
+    stud_zip varchar(10),
+    primary key (stud_id)
+);
+
+create table be05.course(
+	course_id int not null,
+    course_name varchar(255),
+    primary key(course_id)
+);
+
+create table be05.room(
+	room_id int not null,
+    room_loc varchar(50),
+    room_cap varchar(50),
+    class_id int,
+    primary key (room_id)
+    -- foreign key (class_id) references class(class_id)
+);
+
+create table be05.class(
+	class_id int not null,
+    class_name varchar(255),
+    prof_id int,
+    course_id int,
+    room_id int,
+    primary key (class_id),
+    foreign key (prof_id) references professor(prof_id),
+    foreign key (course_id) references course(course_id),
+    foreign key (room_id) references room(room_id)
+);
+
+alter table be05.room
+add foreign key (class_id) references class(class_id);
+
+create table be05.enroll(
+	stud_id int not null,
+    class_id int not null,
+    grade varchar(3),
+    primary key (stud_id, class_id),
+    foreign key (stud_id) references student(stud_id),
+    foreign key (class_id) references class(class_id)
+);
+

sol-3.sql

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+-- những cặp student-professor có dạy học nhau và số lớp mà họ có liên quan
+select p.prof_id, e.stud_id, count(*) as 'no_of_class'
+from professor as p join class as c on p.prof_id = c.prof_id
+join enroll as e on e.class_id
+group by p.prof_id, e.stud_id;
+
+-- những course (distinct) mà 1 professor cụ thể đang dạy
+select distinct c.course_id, c.course_name, p.prof_id, p.prof_fname, p.prof_lname
+from professor as p join class as cl on p.prof_id = cl.prof_id
+join course as c on cl.course_id = c.course_id;
+
+-- những course (distinct) mà 1 student cụ thể đang học
+select distinct c.course_id, c.course_name, s.stud_id, s.stud_fname, s.stud_lname
+from student as s join enroll as e on s.stud_id = e.stud_id
+join class as cl on e.class_id = cl.class_id
+join course as c on c.course_id = cl.course_id;
+
+-- điểm số là A, B, C, D, E, F tương đương với 10, 8, 6, 4, 2, 0
+
+-- điểm số trung bình của 1 học sinh cụ thể (quy ra lại theo chữ cái, và xếp loại học lực (weak nếu avg < 5, average nếu >=5 < 8, good nếu >=8 )
+select t.stud_id, t.stud_fname, t.stud_lname,
+case when t.avg_grade_num < 5 then 'Weak'
+	 when t.avg_grade_num >= 8 then 'Good'
+	 else 'Average'
+	end as classification,
+case when t.avg_grade_num = 10 then 'A'
+	 when t.avg_grade_num = 8 then 'B'
+     when t.avg_grade_num = 6 then 'C'
+     when t.avg_grade_num = 4 then 'D'
+     when t.avg_grade_num = 2 then 'E'
+     when t.avg_grade_num = 0 then 'F'
+end as avg_grade_letter
+from (
+	select s.stud_id, s.stud_fname, s.stud_lname, avg(e.grade_num) as 'avg_grade_num'
+    from (
+		select * , case when grade = 'A' then 10
+						when grade = 'B' then 8
+						when grade = 'C' then 6
+						when grade = 'D' then 4
+						when grade = 'E' then 2
+						when grade = 'F' then 0
+					end as grade_num
+		from enroll
+	) as e join student as s on s.stud_id = e.stud_id 
+    group by s.stud_id
+) as t;
+
+-- điểm số trung bình của các class (quy ra lại theo chữ cái)
+select t.class_id, t.class_name,
+case when t.avg_grade_num = 10 then 'A'
+	 when t.avg_grade_num = 8 then 'B'
+     when t.avg_grade_num = 6 then 'C'
+     when t.avg_grade_num = 4 then 'D'
+     when t.avg_grade_num = 2 then 'E'
+     when t.avg_grade_num = 0 then 'F'
+end as avg_grade_letter
+from (
+	select cl.class_id, cl.class_name, avg(e.grade_num) as 'avg_grade_num'
+    from (
+		select * , case when grade = 'A' then 10
+						when grade = 'B' then 8
+						when grade = 'C' then 6
+						when grade = 'D' then 4
+						when grade = 'E' then 2
+						when grade = 'F' then 0
+					end as grade_num
+		from enroll
+	) as e join class as cl on cl.class_id = e.class_id 
+    group by cl.class_id
+) as t;
+
+-- điểm số trung bình của các course (quy ra lại theo chữ cái)
+select t.course_id, t.course_name,
+case when t.avg_grade_num = 10 then 'A'
+	 when t.avg_grade_num = 8 then 'B'
+     when t.avg_grade_num = 6 then 'C'
+     when t.avg_grade_num = 4 then 'D'
+     when t.avg_grade_num = 2 then 'E'
+     when t.avg_grade_num = 0 then 'F'
+end as avg_grade_letter
+from (
+	select c.course_id, c.course_name, avg(e.grade_num) as 'avg_grade_num'
+    from (
+		select * , case when grade = 'A' then 10
+						when grade = 'B' then 8
+						when grade = 'C' then 6
+						when grade = 'D' then 4
+						when grade = 'E' then 2
+						when grade = 'F' then 0
+					end as grade_num
+		from enroll
+	) as e join class as cl on cl.class_id = e.class_id 
+    join course as c on c.course_id = cl.course_id
+    group by c.course_id
+) as t