I have the following 3 tables for students and I need to find the names of students who currently are enrolled in classes that meet at the same time
student(**snum**, sname, major, level, age)
class(**cname**, meets_at, room)
enroll(**snum**, **cname**)
The keys for each table is in bold.
I have tried the folling code and I'm not sure whether I'm close to the correct answer here.
select s.sname
from student s
join
( select c.cname
, c.meets_at
, (count(*)
from class c
having count( * ) > 1
) e
on c.cname = e.cname
and s.snum = e.snum;
I would think of this as joining on students with meetsat. So, this gets students with their class times:
select s.sname, c.meets_at
from students s join
enrolls e
on s.snum = e.snum join
classes c
on c.cname = e.cname;
Then, to get the duplicates, use aggregation and filter using having:
select s.snum, s.sname, c.meets_at, count(*) as cnt
from students s join
enrolls e
on s.snum = e.snum join
classes c
on c.cname = e.cname
group by s.snum, sname, c.meets_at
having count(*) >= 2;
Note that this includes the ids as well as the name, because two students could have the same name.
Finally, a student could have multiple pairs of classes that conflict, but you only want to see the student once. Although the above is probably sufficient for your purposes, a more accurate solution for the stated problem would be:
select distinct s.sname
from students s join
enrolls e
on s.snum = e.snum join
classes c
on c.cname = e.cname
group by s.snum, sname, c.meets_at
having count(*) >= 2;
select s.snum, s.sname, c.meets_at ,count(*) as cnt into #tempStudents
from students s
join enrolls e on s.snum = e.snum
join classes c on c.cname = e.cname;
Put the whole data in temporary table
select sname from #tempStudents
group by snum,sname ,meets_at
having cnt >=2
Now apply filtration on temporary table for getting desire data
and if u need distinct name of student put Distinct keyword before sname.
Related
I have two tables:
Class: cid, name, location
Student: sid, name, gender, classID
I am attempting to use a select statement to display the class name along with the total number of students in the class. I'm also trying to exclude any class with less than 10 students from the table.
SELECT
c.name as className,
count(s.sid) as totalStudents
FROM Class c
JOIN Student s ON s.classID = c.cid
GROUP BY c.id
HAVING count(s.sid) >= 10
select a.name, count(*)
from Class as a
inner join Student as b on b.ClassID = a.cid
group by a.name
having count(*) >= 10;
This sample code her just figures out the grade average for table 3, not the true GPA : SELECT *
FROM (
SELECT AVG(g.Grade) as average_grade, g.SSN
FROM Grade g
group by g.SSN) a
inner join Student s on a.ssn = s.ssn;
Tying to figure out the correct formula: Here is what I have came up with but it is not correct
SELECT *
FROM (
SELECT SUM(Grade*CreditHour)/(SUM(CreditHour) as average_grade, g.SSN
FROM Grade g
group by g.SSN) a
inner join Student s on a.ssn = s.ssn;
Need some help stuck on this problem?
It looks to me as if you simply forgot to join the grade table with the course table. Or am I missing something?
SELECT *
FROM
(
SELECT
SUM(g.Grade*c.CreditHour) / SUM(c.CreditHour) as average_grade,
g.SSN
FROM Grade g
INNER JOIN Course c ON c.cno = g.cno
GROUP BY g.SSN
) a
INNER JOIN Student s ON a.ssn = s.ssn;
I have two tables; One that contains students names and sids and the other is a "take" table containing the sids of students and their grades.
I want to show the names of students who have average greater than that of a student name "Peter-Parker".
I have tried the query below, but it doesn't work.
SELECT s.sid, s.fname, s.lname
FROM student s, take t
WHERE s.sid = t.sid AND AVG(t.grade) > ALL(
SELECT AVG(grade)
FROM take, student
WHERE student.fname = 'Ali' and student.lname='Demir');
WITH AliAv(avg) AS
(SELECT AVG(grade) from take t, student s
where t.sid = s.sid ands.fname = 'Ali' and s.lname = 'Demir')
select student.sid, student.fname, student.lname
from student, take
where student.sid = take.sid Group by student.sid
having avg(take.grade) > AliAv.av;
SELECT s.sid, s.fname, s.lname, AVG(t.grade) AS average
FROM student AS s
JOIN take AS t ON t.sid = s.sid
GROUP BY s.sid
HAVING average > (
SELECT AVG(t2.grade)
FROM student AS s2
JOIN take AS t2 ON t2.sid = s2.sid
WHERE s2.fname = 'Peter' and s2.lname = 'Parker'
)
This works in SQL Server, I don't know if the syntax is valid in MySQL:
SELECT *
FROM Student s
WHERE
(SELECT AVG(Grade) FROM Take WHERE SID=s.ID) > (SELECT AVG(Grade) FROM Take WHERE SID = (SELECT SID FROM Student WHERE FName='Peter' AND LName='Parker'))
I am having trouble trying to create a query to:
Select all the students who have not completed all peer review's for a particular week.
background: Each week, every student must peer review their peers in the same group.
Each group can be a different size, which is the problem I am having.
this is my current test data:
Table 1: peer review table
Table 2: student table.
This is my inital query, groups all the students based on the amount of peer review's they've made. I now need to to check if the count(*) is less than the size of the group for each student :
SELECT *
FROM peerreview
RIGHT JOIN student
ON student. studentID = peerreview.reviewer
WHERE week = 11
GROUP BY studentID
HAVING Count(*) < ????
Following query will return the student which has reviewed all the students in same group.
SELECT a.reviewer,
a.groupid
FROM (SELECT student2.studentID AS reviewer,
student1.groupid,
Count(*) AS cnt
FROM student student1
INNER JOIN peerreview
ON student1.studentID = peerreview.reviewee
INNER JOIN STUDENT STUDENT2
ON student2.studentID = peerreview.reviewer
WHERE student2.groupid = student2.groupid
AND peerreview.week = 11
GROUP BY student1.groupid,
student2.studentID) a
INNER JOIN (SELECT groupid,
Count(*) - 1 AS cnt
FROM student
GROUP BY groupid) b
ON a.groupid = b.groupid
AND a.cnt = b.cnt
See SqlFiddle
Select S.StudentId As Reviewer
, S1.StudentId As StudentYetToBeReviewed
, Weeks.WeekNum
From Student As S
Join Student As S1
On S1.GroupId = S.GroupId
And S1.StudentId <> S.StudentId
Cross Join (
Select 7 As WeekNum
Union All Select 11
) As Weeks
Where Not Exists (
Select 1
From PeerReview As P1
Where P1.reviewee = S1.StudentId
And P1.Week = Weeks.WeekNum
)
Order By WeekNum, reviewer
This provides you a list, by week, of the reviewer and the person they need to review. In the real solution, you would want to replace the Cross Join of weeks with a distinct list of weeks in which reviews should happen.
SQL Fiddle version
select distinct s1.*
from student s1 inner join student s2 on s1.groupId = s2.groupeId
left join peerreview pr on pr.revieweer = s1.studentId
and pr.reviewee = s2.studentId
where pr.Week = ? and pr.revieweer is null and s1.studentId <> s2.studentId
I am trying to select the classes with maximum enrollment in each department from a table with the following structure:
Courses: cid, dept, name
Enrollment: cid, sid
The idea would be to count all the enrollments in each class, and find the maximum in each department. Unfortunately, I'm having trouble with the maximum-count combination.
My query was going to look something like:
SELECT c.name, MAX(COUNT(*) FROM Enrollment E WHERE E.cid = C.cid)
FROM Courses C
GROUP BY C.dept
But I can't figure out how to get the MAX-COUNT syntax to work properly. I've tried a lot of different examples from Google and StackOverflow and none of them worked for me. MySQL says the syntax is wrong.
I like nested queries for this kind of problem. First select the enrollment counts grouped per class. Then find the max enrollment count grouped per department:
SELECT MAX(cnt) cnt, dept FROM
(
SELECT COUNT(*) cnt, dept, C.cid
FROM Courses C
INNER JOIN Enrollment E on C.cid = E.cid
GROUP BY cid, dept
) a
GROUP BY dept
There is no declaration of E, so you can't use E.cid
So, either you do this
SELECT c.name, COUNT(c.*) as count
FROM Courses C
GROUP BY C.dept
Or,
SELECT c.name, MAX(SELECT COUNT(*) FROM Enrollment E WHERE E.cid = C.cid)
FROM Courses C
GROUP BY C.dept
SELECT MAX(cnt) FROM (
SELECT c.name, COUNT(E.*) AS cnt FROM Enrollment E
INNER JOIN Courses C ON E.cid = C.cid
GROUP BY C.dept
) final