Analytical Query in SQL for MIN, MAX, and AVG - sql

Question

I am trying to figure out a query for this question: for each major, list the number of students, minimum GPA, maximum GPA, average GPA, minimum age, maximum age, and average age. (Show GPA with 2 decimal points, age with no decimal points. You may find it useful to create a view with one of the previous queries for this one.)
This is the script to create the table for SQL!
REM drop all the tables. Note that you need to drop the
REM dependent table first before dropping the base tables.
drop table Reg;
drop table Student;
drop table Course;
REM Now create all the tables.
create table Student
(
sid char(10) primary key,
sname varchar(20) not null,
gpa float,
major char(10),
dob DATE
);
create table Course
(
cno char(10) primary key,
cname varchar(20) not null,
credits int,
dept char(10)
);
create table Reg
(
sid references Student(sid) on delete cascade,
cno references Course(cno) on delete cascade,
grade char(2),
primary key (sid, cno)
);
REM Now insert all the rows.
insert into Student values ('111', 'Joe', 3.5 , 'MIS', '01-AUG-2000');
insert into Student values ('222', 'Jack', 3.4 , 'MIS', '12-JAN-1999');
insert into Student values ('333', 'Jill', 3.2 , 'CS', '15-MAY-1998');
insert into Student values ('444', 'Mary', 3.7 , 'CS', '17-DEC-2001');
insert into Student values ('555', 'Peter', 3.8 , 'CS', '19-MAR-1999');
insert into Student values ('666', 'Pat', 3.9, 'Math', '31-MAY-2000');
insert into Student values ('777', 'Tracy', 4.0, 'Math', '18-JUL-1997');
insert into Course values ('c101', 'intro', 3 , 'CS');
insert into Course values ('m415', 'database', 4 , 'Bus');
insert into Course values ('m215', 'programming', 4 , 'Bus');
insert into Course values ('a444', 'calculus', 3 , 'Math');
insert into Reg values ('111', 'c101', 'A');
insert into Reg values ('111', 'm215', 'B');
insert into Reg values ('111', 'm415', 'A');
insert into Reg values ('222', 'm215', 'A');
insert into Reg values ('222', 'm415', 'B');
insert into Reg values ('333', 'c101', 'A');
insert into Reg values ('444', 'm215', 'C');
insert into Reg values ('444', 'm415', 'B');
insert into Reg values ('555', 'c101', 'B');
insert into Reg values ('555', 'm215', 'A');
insert into Reg values ('555', 'm415', 'A');
insert into Reg values ('666', 'c101', 'A');
This is what I have so far:
SELECT major,
count(distinct SID) as students,
round(min(gpa), 2),
round(max(gpa), 2),
round(avg(gpa), 2),
trunc(min(sysdate - dob)/365) as min_age,
trunc(max(sysdate - dob)/365) as max_age,
trunc(avg(sysdate - dob)/365) as avg_age,
FROM Student
GROUP BY MAJOR;

Answer 1

According to your input I've made a query that I belive will show you the results. (It was kind hard to read the tables the way you posted it). The syntax may differ according to your DBMS (SQL Server, MySQL, REdshift, Postgres, etc)
Here is the query:
SELECT major,
COUNT(*) as students,
ROUND(MIN(gpa), 2) as min_gpa,
ROUND(MAX(gpa), 2) as max_gpa,
ROUND(AVG(gpa), 2) as avg_gpa,
MIN(DATEDIFF(year, current_date, dob)) as min_age,
MAX(DATEDIFF(year, current_date, dob)) as max_age,
AVG(DATEDIFF(year, current_date, dob)) as avg_date
FROM students st left join Course co on co.dept = st.major
GROUP BY major

Answer 2

Your query is completely fine (just remove comma(,) after avg_age.
SELECT major,
count(distinct SID) as students,
round(min(gpa), 2) as MinGPA,
round(max(gpa), 2) as MaxGPA,
round(avg(gpa), 2) as AvgGPA,
round(min(sysdate - dob)/365,0) as min_age,
round(max(sysdate - dob)/365,0) as max_age,
round(avg(sysdate - dob)/365,0) as avg_age
FROM Student
GROUP BY MAJOR;
You can also use months_between() with floor() to get the same result:
select * from student;
SELECT major,
count(distinct SID) as students,
round(min(gpa), 2) as MinGPA,
round(max(gpa), 2) as MaxGPA,
round(avg(gpa), 2) as AvgGPA,
floor(min(months_between(trunc((sysdate)), dob)) /12) as min_age,
floor(max(months_between(trunc((sysdate)), dob)) /12) as max_age,
floor(avg(months_between(trunc((sysdate)), dob)) /12) as avg_age
FROM Student
GROUP BY MAJOR;