Query that gets students with their courses in same row - sql

Question

I need a query that will get students whom get Course1, Course2 and Course3. I can query it like that:
SELECT k.name as firstname, k.surname as lastname, k.Email
FROM Students k
JOIN StudentCourses dn ON dn.StudentID = k.StudentID
WHERE dn.CourseID IN
(SELECT CourseID FROM Courses WHERE CourseName IN ('Course1','Course2','Course3'))
But i need a result set like that: Name, Surname, Email, Course1, Course2, Course3. No multiple rows for a student, one row and write course name if students get that course.
In fact i can imagine how to write that query (with subselects), wonder about better alternatives.

Answer 1

You can use the PIVOT table operator to do this, something like this:
WITH CTE
AS
(
SELECT
k.name as firstname,
k.surname as lastname,
k.Email,
c.CourseName, c.CourseID
FROM Students k
JOIN StudentCourses dn ON dn.StudentID = k.StudentID
INNER JOIN Courses c ON dn.CourseID = c.CourseID
WHERE c.CourseName IN ('Course1','Course2','Course3')
)
SELECT *
FROM CTE AS c
PIVOT
(
MAX(CourseID)
FOR CourseName IN ([Course1], [Course2], [Course3])
) u;
SQL Fiddle Demo
Note that, Since you don't have other columns to display under each column of course for each students, this query will display CourseID value for each course name, null if the student doesn't have this course. You should choose to display more appropriate column instead, like mark for example:
WITH CTE
AS
(
SELECT
k.name as firstname,
k.surname as lastname,
k.Email,
c.CourseName, dn.Mark
FROM Students k
JOIN StudentCourses dn ON dn.StudentID = k.StudentID
INNER JOIN Courses c ON dn.CourseID = c.CourseID
WHERE c.CourseName IN ('Course1','Course2','Course3')
)
SELECT *
FROM CTE AS c
PIVOT
(
MAX(Mark)
FOR CourseName IN ([Course1], [Course2], [Course3])
) u;
Updated SQL Fiddle Demo
This will give you:
| firstname | lastname | Email | Course1 | Course2 | Course3 |
|-----------|----------|-------|---------|---------|---------|
| StudentA | test | test | 19 | 20 | 15 |
| StudentB | test | test | 16 | 17 | 20 |
| StudentC | test | test | 20 | 19 | 15 |
Also note that, you should be careful about the columns you choose in the anchor query:
...
SELECT
k.name as firstname,
k.surname as lastname,
k.Email,
c.CourseName, dn.Mark
...
Because the PIVOT table operator will group by all the columns except the columns you listed and used to pivot:
MAX(CourseID)
FOR CourseName IN
So in your case, it will group by firstname, lastname, Email.

Answer 2

I think you can use a better query than yours and use MAX(CASE ...) to achieve your expected result like this:
SELECT k.name as firstname, k.surname as lastname, k.Email,
MAX(CASE WHEN c.CourseName = 'Course1' THEN 'Yes' ELSE 'No' END) As Course1,
MAX(CASE WHEN c.CourseName = 'Course2' THEN 'Yes' ELSE 'No' END) As Course2,
MAX(CASE WHEN c.CourseName = 'Course3' THEN 'Yes' ELSE 'No' END) As Course3
FROM Students k
JOIN StudentCourses dn ON dn.StudentID = k.StudentID
JOIN Courses c ON c.CourseID = dn.CourseID AND c.CourseName Like 'Course[1-3]'
GROUP BY k.name, k.surname, k.Email;