Write SQL query for: For all instructors who are advisors of atleast 2 students,
ID: 3752152 • Letter: W
Question
Write SQL query for:
For all instructors who are advisors of atleast 2 students, increase their salary by 50000.
//University DDL statements
create table classroom
(building varchar(15),
room_number varchar(7),
capacity numeric(4,0),
primary key (building, room_number)
);
create table department
(dept_name varchar(20),
building varchar(15),
budget numeric(12,2) check (budget > 0),
primary key (dept_name)
);
create table course
(course_id varchar(8),
title varchar(50),
dept_name varchar(20),
credits numeric(2,0) check (credits > 0),
primary key (course_id),
foreign key (dept_name) references department
on delete set null
);
create table instructor
(ID varchar(5),
name varchar(20) not null,
dept_name varchar(20),
salary numeric(8,2) check (salary > 29000),
primary key (ID),
foreign key (dept_name) references department
on delete set null
);
create table section
(course_id varchar(8),
sec_id varchar(8),
semester varchar(6)
check (semester in ('Fall', 'Winter', 'Spring', 'Summer')),
year numeric(4,0) check (year > 1701 and year < 2100),
building varchar(15),
room_number varchar(7),
time_slot_id varchar(4),
primary key (course_id, sec_id, semester, year),
foreign key (course_id) references course
on delete cascade,
foreign key (building, room_number) references classroom
on delete set null
);
create table teaches
(ID varchar(5),
course_id varchar(8),
sec_id varchar(8),
semester varchar(6),
year numeric(4,0),
primary key (ID, course_id, sec_id, semester, year),
foreign key (course_id,sec_id, semester, year) references section
on delete cascade,
foreign key (ID) references instructor
on delete cascade
);
create table student
(ID varchar(5),
name varchar(20) not null,
dept_name varchar(20),
tot_cred numeric(3,0) check (tot_cred >= 0),
primary key (ID),
foreign key (dept_name) references department
on delete set null
);
create table takes
(ID varchar(5),
course_id varchar(8),
sec_id varchar(8),
semester varchar(6),
year numeric(4,0),
grade varchar(2),
primary key (ID, course_id, sec_id, semester, year),
foreign key (course_id,sec_id, semester, year) references section
on delete cascade,
foreign key (ID) references student
on delete cascade
);
create table advisor
(s_ID varchar(5),
i_ID varchar(5),
primary key (s_ID),
foreign key (i_ID) references instructor (ID)
on delete set null,
foreign key (s_ID) references student (ID)
on delete cascade
);
create table time_slot
(time_slot_id varchar(4),
day varchar(1),
start_hr numeric(2) check (start_hr >= 0 and start_hr < 24),
start_min numeric(2) check (start_min >= 0 and start_min < 60),
end_hr numeric(2) check (end_hr >= 0 and end_hr < 24),
end_min numeric(2) check (end_min >= 0 and end_min < 60),
primary key (time_slot_id, day, start_hr, start_min)
);
create table prereq
(course_id varchar(8),
prereq_id varchar(8),
primary key (course_id, prereq_id),
foreign key (course_id) references course
on delete cascade,
foreign key (prereq_id) references course
);
Explanation / Answer
Query:
UPDATE instructor SET salary=salary+50000 WHERE ID in (
SELECT i_ID, COUNT(*) as count FROM advisor GROUP BY i_ID HAVING count>1 );
Explanation:
First get all the instructors who are advisors of atleast 2 students from 'advisor table' using GROUP BY and HAVING in subquery:
SELECT i_ID, COUNT(*) as count FROM advisor GROUP BY i_ID HAVING count>1
Using the above as a subquery, now update the salary in the 'instructor table' using where clause & IN operator.
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