I have three tables:
Student(StudentID, StudentName)
Course(CourseID, CourseName)
StudentCourse(StudentID, CourseID) -- junction table to assign courses to students
How would I query to get the favourite course--"the course which has highest number of students enrolled"?
SQLFiddle
Try it by using TOP...WITH TIES
SELECT TOP 1 WITH TIES c.CourseName,
COUNT(c.CourseID) totalCount
FROM student a
INNER JOIN studentcourse b
ON a.studentID = b.studentID
INNER JOIN course c
ON b.courseID = c.courseID
GROUP BY c.CourseName
ORDER BY totalCount DESC
WITH TIES show the records that have the same highest number of counts.
SQLFiddle Demo
SELECT TOP 1 WITH TIES COURSEID
FROM STUDENTCOURSE
GROUP BY COURSEID
ORDER BY Count(*) DESC
Related
I have this tables:
Student - Id, FirstName, LastName, Age
Group - Id, Name
Student_Group - Student_Id, Group_Id
I need to find least group of student. I have tried many times. I would be so glad if somebody helped.
Have you tried to do
SELECT top 1 g.name
FROM group g INNER JOIN Student_group sg ON g.id = sg.Group_Id
WHERE count(sg.student_id) >0
ORDER BY count(sg.student_id)
GROUP BY sg.group_id
?
If you want also the groups with 0 students you should to do
SELECT top 1 g.name
FROM group g INNER JOIN Student_group sg ON g.id = sg.Group_Id
ORDER BY count(sg.student_id)
GROUP BY sg.group_id
--If you just need the group with the least members,
--Group By and Count will work to find the Group with the least members
--Then use select top 1 record and order by GroupCount Ascending
SELECT TOP 1 Group_Id, COUNT(Group_Id) AS [GroupCount]
FROM Student_Group
GROUP BY Group_Id
ORDER BY [GroupCount]
I am having trouble returning the most common course
Question is: Write a Query to return the CourseName of the most common course
Tables
StudentCourses:
StudentCourseID
StudentID
CourseID
Courses:
CourseID
CourseName
I have this
SELECT CourseName
From Courses c
WHERE CourseID = (SELECT Count(CourseID) AS Course_Value
FROM StudentCourses
Group BY CourseID
Order BY Course_Value DESC
LIMIT 1;
I know it isnt correct but am i correct using COUNT to find the most popular course correctly?
SELECT Top 1 CourseName
FROM Courses
JOIN StudentCourses
ON Courses.CourseId = StudentCourses.CourseId
GROUP BY CourseName
ORDER BY Count(CourseName) DESC
For this type of question, learn to use explicit join and top:
select top (1) c.courseid, c.coursename, count(*) as cnt
from studentcourses sc join
courses c
on sc.courseid = c.courseid
group by c.courseid, c.coursename
order by count(*) desc;
If you want ties, then use top with ties.
I have a table of students and a table of books that they borrowed. I need to find a student who borrowed the most books and show titles of these books.
Currently I have a list of students and number of books that each student borrowed, sorted descending. I can get the student who borrowed the most by using Top 1.
SELECT TOP 1 Students.Name, Students.LastName, Count(Books.Title) AS BorrowedBooksCount
FROM (Meldunek INNER JOIN Students ON Meldunek.pesel = Students.pesel)
INNER JOIN Books
ON Students.pesel = Books.pesel
GROUP BY Students.Name, Students.LastName
ORDER BY Count(Books.Title) DESC;
How to show names of books of a student who borrowed the most books?
To get the student who borrowed the most books:
select top 1 m.pesel
from Meldunek as m
group by m.pesel
order by count(*) desc;
You can use this in a where clause for filtering. But you should take into account that multiple students might have the same value. So, use in rather than =:
where s.pesel in (select top 1 m.pesel
from Meldunek as m
group by m.pesel
order by count(*) desc
);
This logic can be inserted into your query, so you return only the top borrowing students.
The complete query looks like:
select s.Name, s.LastName, b.Title
from (Meldunek as m inner join
Students s
on m.pesel = s.pesel
) inner join
Books as b
on s.pesel = b.pesel
where s.pesel in (select top 1 m2.pesel
from Meldunek as m2
group by m2.pesel
order by count(*) desc
);
There are three tables:
A table about students: s41071030(sno, sname, ssex, sage, sdept)
A table about course: c41071030(cno, cname, cpno, credit)
A table about selecting courses: sc41071030(sno, cno, grade)
Now, I want select the details about a student whose sdept='CS' and he or she has selected the most courses in department 'CS'.
As with any modestly complex SQL statement, it is best to do 'TDQD' — Test Driven Query Design. Start off with simple parts of the question and build them into a more complex answer.
To find out how many courses each student in the CS department is taking, we write:
SELECT S.Sno, COUNT(*) NumCourses
FROM s41071030 S
JOIN sc41071030 SC ON S.Sno = SC.Sno
WHERE S.Sdept = 'CS'
GROUP BY S.Sno;
We now need to find the largest value of NumCourses:
SELECT MAX(NumCourses) MaxCourses
FROM (SELECT S.Sno, COUNT(*) NumCourses
FROM s41071030 S
JOIN sc41071030 SC ON S.Sno = SC.Sno
WHERE S.Sdept = 'CS'
GROUP BY S.Sno
)
Now we need to join that result with the sub-query, so it is time for a CTE (Common Table Expression):
WITH N AS
(SELECT S.Sno, COUNT(*) NumCourses
FROM s41071030 S
JOIN sc41071030 SC ON S.Sno = SC.Sno
WHERE S.Sdept = 'CS'
GROUP BY S.Sno
)
SELECT N.Sno
FROM N
JOIN (SELECT MAX(NumCourses) MaxCourses FROM N) M
ON M.MaxCourses = N.NumCourses;
And we need to get the student details, so we join that with the student table:
WITH N AS
(SELECT S.Sno, COUNT(*) NumCourses
FROM s41071030 S
JOIN sc41071030 SC ON S.Sno = SC.Sno
WHERE S.Sdept = 'CS'
GROUP BY S.Sno
)
SELECT S.*
FROM s41071030 S
JOIN N ON N.Sno = S.Sno
JOIN (SELECT MAX(NumCourses) MaxCourses FROM N) M
ON M.MaxCourses = N.NumCourses;
Lightly tested SQL: you were warned. To test, run the component queries, making sure you get reasonable results each time. Don't move on to the next query until the previous one is working correctly.
Note that the courses table turns out to be immaterial to the query you are solving.
Also note that this may return several rows if it turns out there are several students all taking the same number of courses and that number is the largest number that any student is taking. (So, if there are 3 students taking 7 courses each, and no student taking more than 7 courses, then you will see 3 rows in the result set.)
Aggregate sc41071030 rows to get the counts.
Join the results to s41071030 to:
filter rows on sdept;
get student details;
RANK() the joined rows on the count values.
Select rows with the ranking of 1.
WITH
aggregated AS (
SELECT
sno,
COUNT(*) AS coursecount
FROM
sc41071030
GROUP BY
sno
),
ranked AS (
SELECT
s.*,
RANK() OVER (ORDER BY agg.coursecount DESC) AS rnk
FROM
s41071030 s
INNER JOIN aggregated agg ON s.sno = agg.sno
WHERE
s.sdept = 'CS'
)
SELECT
sno,
sname,
ssex,
sage,
sdept
FROM
ranked
WHERE
rnk = 1
;
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)