REVISED:
Okay, thanks to all of your input, I figured out what I was doing wrong (sorry guys). I am grabbing the courseID which counts as a section NOT an actual course. For me to grab the actual courseName, I have to go over to the Course Table.
So now I have StudentID from Enrollment and CourseNum from Course that need to be used to count. I'll try and work with what you guys have provided to see if I can come up with the results.
EDIT:
Here's my revised SQL. This provides me with the total courses for each student. I'm getting there:
SELECT Count(DISTINCT Course.courseNum), Grades.studentID
FROM Grades INNER JOIN
Course ON Grades.courseID = Course.courseID
GROUP BY Grades.studentID;
Final Code just in case those who care:
SELECT COUNT(NumCourses) FROM
(SELECT Count(DISTINCT Course.courseNum)AS NumCourses
FROM Grades INNER JOIN
Course ON Grades.courseID = Course.courseID
GROUP BY Grades.studentID
HAVING Count(DISTINCT Course.courseNum) = 1) a;
Try this:
select count(studentId), count(courseId) from enrolment group by courseId having (count(courseId) = 2);
To get the total number of students on 4+ courses, this is the SQL:
SELECT COUNT(CourseCount) AS CourseCount
FROM (
SELECT StudentID, COUNT(CourseID) AS CourseCount
FROM enrollment
GROUP BY StudentID
HAVING (COUNT(CourseID) >= 4)) AS T
It is much simpler to get the student count using a second query.
SELECT COUNT(NumCourses) AS NumStudents, NumCourses FROM (SELECT COUNT(courseID) AS NumCourses FROM enrollment GROUP BY courseID HAVING COUNT(courseID) = 4) As SomeTableAlias
select count(*)
from (select student_id from enrollment group by student_id having count(*) = 4)
The inner query gives you the IDs of the students who enrolled in exactly 4 courses then I count them.
I thought you wanted the number of students who are enrolled in exactly four courses.
If you want to count the number of students and the number of courses, do this:
SELECT * FROM (SELECT COUNT(*) AS NumStudents FROM (SELECT DISTINCT studendid FROM enrollment)), (SELECT COUNT(*) AS NumCourses FROM (SELECT DISTINCT courseid FROM enrollment))
SELECT COUNT(*) FROM
(SELECT COUNT(*) FROM enrollment
GROUP BY studentid HAVING COUNT(*) = 4)
Related
I have the following tables:
Students (id, name, surname, study_year, department_id)
Courses(id, name)
Course_Signup(id, student_id, course_id, year)
I want to display the courses to which at least 10 students have signed up for, only using subqueries (no group-by, join or set operations). This could be easily implemented using data aggregation and join:
SELECT c.name, COUNT(csn.course_id)
FROM Course_Signup csn
JOIN Courses c
ON csn.course_id = c.id
GROUP BY c.name
HAVING COUNT(csn.course_id) >= 10
But how would I do this only using subqueries? Is there any other way, other than COUNT, to get the number of courses? Thank you, in advance!
You can use a correlated sub-query to retrieve the name:
SELECT (SELECT c.name FROM Courses c WHERE csn.course_id = c.id) AS name,
COUNT(*)
FROM Course_Signup csn
GROUP BY
course_id
HAVING COUNT(*) >= 10
Note: you should also GROUP BY the primary key the uniquely identifies the course as there may be two courses with the same name.
If you also don't want to use GROUP BY then:
SELECT name
FROM Courses c
WHERE 10 <= ( SELECT COUNT(*)
FROM Course_Signup csn
WHERE csn.course_id = c.id )
or, to also get the number of sign-ups:
SELECT *
FROM (
SELECT name,
( SELECT COUNT(*)
FROM Course_Signup csn
WHERE csn.course_id = c.id ) AS num_signups
FROM Courses c
)
WHERE num_signups >= 10;
You could do:
SELECT c.name
FROM Courses c
WHERE (
SELECT COUNT(*)
FROM Course_Signup csn
WHERE csn.course_id = c.id
) >= 10
which only uses a subquery and has no group-by, join or set operations.
fiddle
If you wanted the actual count in the result set then you would need to repeat the subquery in the select list.
You might also need to do COUNT(DISTINCT cs.student_id) if there might be duplicates; particularly if the same student can sign up in multiple years - but then you might want to restrict to a single year anyway.
Based off the following table schema, I want to be able to select the sum of the maximum of each submission. A student can have multiple submissions for a contest, so their total score is the sum of the maximum score of each contest. Right now my query selects student_id, name, and maximum score of all their contests, how can I get the sum of the max of all their contest? The expected output based on the input should be:
select student_id, name, max(score) as TotalScore
from students2 as st
join submissions as s
where st.student_id = s.student_id
group by st.student_id, name
having count(*) > 1
order by TotalScore desc;
select student_id, name, sum(TotalScore) total_sum
from (select st.student_id student_id
, name
, max(score) as TotalScore
from students as st
join submissions as s
on st.student_id = s.student_id
group by s.contest_id, s.student_id)
group by student_id;
Here is a demo
I have started to create a demo before your sample data...
From your text in your question I did not understood what do you need having count(*) > 1 for so I did not used it.
Please note: I have used students as the name of the table and not students2.
Use two levels of aggregation:
select student_id, name, sum(max_score) as TotalScore
from students2 st join
(select s.student_id, max(score) as max_score
from submissions s
group by s.student_id
) s
on st.student_id = s.student_id
group by st.student_id, name
having count(*) > 1;
order by TotalScore desc;
I notice that your FROM clause is using JOIN but missing the ON clause. You should get used to always including that.
I have following schema:
Students(sid, firstname, lastname, status, gpa, email)
Courses(dept_code, course#, title)
Classes(classid, dept_code, course#, sect#, year, semester, limit, class_size)
Enrollments(sid, classid, lgrade)
I need some help to find out all the students who received an A for every course taken.
I might suggest doing this with an aggregation:
select e.sid
from enrollement e
group by e.sid
having min(lgrade) = max(lgrade) and min(lgrade) = 'A';
try this
select * from students
where sid not in (select distinct sid from enrollement where coalesce (lgrade,'X') <> 'A')
It means: take all students where none of his/her grade is other than A
if you wanna to get also the name of the class and course, you have to join also both tables
Try not to overthink this:
SELECT s.*
FROM STUDENTS s
WHERE s.GPA = 4.0
That'll work for the A=4, B=3, C=2, D=1, F=0 case (standard American grading system).
For non-standard systems (such as my kids high school where A=5 for honors and advanced placement classes) we can't trust the GPA:
SELECT s.*
FROM STUDENTS s
INNER JOIN (SELECT SID, COUNT(*) AS CLASS_COUNT
FROM ENROLLMENTS
GROUP BY SID) cc
INNER JOIN (SELECT SID, COUNT(*) AS A_GRADE_COUNT
FROM ENROLLMENTS
WHERE LGRADE = 'A'
GROUP BY SID) ag
ON ag.SID = s.SID
WHERE CLASS_COUNT = A_GRADE_COUNT
Best of luck.
I think this is the clearest:
select e.sid
from enrollement e
group by e.sid
having count(case when lgrade = 'A' then 1 else 0 end) = count(*) and count(*) > 0
Hello there, I have a questions for you guys. You see enrollment and student table in images below. I want to run a query getting first and last name from student table but students should belong to a section with less than 5 enrolled students.
Does that make any sense? If i am not clear please do ask me a question. Any help with this is greatly appreciated.
Why access one table more than once, if you can save some work by using analytic functions?
select
first_name, last_name
from
(
select
s.first_name, s.last_name, count(*) over(partition by e.section_id) as enrollment_count
from
student s
join enrollment e using (student_id)
)
where
enrollment_count < 5;
This should work.
SELECT s.FIRST_NAME, s.LAST_NAME
FROM student s
WHERE s.STUDENT_ID IN (
SELECT e1.STUDENT_ID
FROM e1.enrollment
WHERE e1.SECTION_ID IN (
SELECT e2.SECTION_ID
FROM e2.enrollment
GROUP BY e2.SECTION_ID HAVING COUNT(DISTINCT e2.STUDENT_ID) < 5
)
)
select t2.first_name, t2.last_name
from table2 t2
inner join
(select student_id from table1 where section_id in
(select section_id from
(select section_id, count(student_id)
from table1
group by section_id
having count(student_id) < 5
)
)
)t1
on t1.student_id = t2.student_id;
Its not pretty, but it should work.
This is a question I could not answer in oracle lab exam.
Given the schema:
(Courses: cid(int), deptid(int)...);
(Students: sid(int), sname (string), deptid(int)...);
(Participation: cid(int), sid(int), ...);
A student can attend courses outside his department.
Need to get the names of the students who take all the courses offered by his department.
How to do this in sqlplus?
SELECT s.sid, s.sname, s.deptid
FROM Students s
INNER JOIN Participation p
ON s.sid = p.sid
INNER JOIN Courses c
ON p.cid = c.cid
AND s.deptid = c.deptid
GROUP BY s.sid, s.sname, s.deptid
HAVING COUNT(DISTINCT c.cid) = (SELECT COUNT(*)
FROM Courses c2
WHERE c2.deptid = s.deptid)
I cannot tesst the query right now, so I don't know if I have a syntactic error, anyway, you can try this idea to achieve your requirements.
SELECT studentName
FROM
(SELECT stu.sname AS studentName,
cour.deptid AS dept,
COUNT(*) AS assistedCoursesByDpt,
Max(cour.total) AS total
FROM students stu,
participation part,
(SELECT cour.deptid,COUNT(*) AS total FROM courses cour GROUP BY cour.deptid
) AS cour
WHERE stu.sid=part.sid
AND part.cid =cour.cid
GROUP BY stu.sid,
cour.deptid
)
WHERE total=assistedCoursesByDpt
Th idea is to create a subquery (cour) that has a new calculated column, the total courses by debt. Then you can compare this total with the agrouped student courses by dept.