Create query with dynamic columns from different tables - sql-server

Question

I'm trying to create a query with dynamic columns, based on data from three tables.
This is the database structure:
STUDENT
studentID int,
studentNumber int,
studentName nvarchar(100).
EXAM:
examID int,
examName varchar(100),
examenDate datetime,
EXAM_REGISTRATION:
studentID int,
examID int,
A record is added to the EXAM_REGISTRATION table when a student has registered for an exam.
What I'm trying to get is a list of all the exams and all the students in a pivot table to see which students have registered for which exams, like this:
Quite frankly I don't know where to start.
I can query everything individually and put it all together but how can I combine it into one query?
I've been researching pivot tables, but every example seems to query only from one table and uses numbers and functions like MIN, AVG etc.
Can someone help me along?

Answer 1

ok lets go
some data to play with
create table #student
(studentID int, studentNumber int, studentName nvarchar(100))
create table #exam
(examID int, examName nvarchar(100), examDate datetime)
create table #examReg
(studentID int, examID int)
insert into #student
values (1, 787878, 'pierwszy')
,(2, 89898, 'drugi')
,(3, 343434, 'trzeci')
,(4, 121212, 'czwarty')
insert into #exam
values (1, 'exPierwszy', GETDATE())
,(2, 'exDrugi', GETDATE())
,(3, 'exTrzeci', GETDATE())
insert into #examReg
values (1,2),(1,3)
, (2,2),(2,3)
,(3,1),(3,2)
,(4,1),(4,2),(4,3)
and now the main part, and explanation
first of all you have to get pivot query
select examName, examDate , min([1]) , min([2]), min([3]) ,min([4])--studentID as studentID, examDate --,studentNumber
from
(select a.studentID , studentNumber, examDate, examName
from #student a
join #examReg b on a.studentID = b.studentID
join #exam c on c.examID = b.examID ) as m
pivot
(min(studentNumber) FOR studentID in ([1],[2],[3],[4])) as t
group by examName, examDate
as you have it , just change it select statement and studentID list in pivot declaration, you have to generate those parts dynamicly , so we just copy previously written query and replace columns with our token
declare #sqlTemplate nvarchar(max) =
'select examName, examDate ##sqlColumnList##
from
(select a.studentID , studentNumber, examDate, examName
from #student a
join #examReg b on a.studentID = b.studentID
join #exam c on c.examID = b.examID ) as m
pivot
(min(studentNumber) FOR studentID in (##sqlStudentIDList##)) as t
group by examName, examDate
'
after that you generate column list and studentID list by concatenting strings in tsql
declare #sqlColumnList nvarchar(max) = ''
select #sqlColumnList += ',min([' + cast(studentID as nvarchar(10)) + ']) as [' + studentName +'(' + cast(studentNumber as nvarchar(10)) + ')]'
from #student
declare #sqlStudentIDList nvarchar(max) = ''
select #sqlStudentIDList += '[' + CAST(studentID as nvarchar(10)) + '],'
from #student
set #sqlStudentIDList = SUBSTRING(#sqlStudentIDList, 0, LEN(#sqlStudentIDList))
select #sqlStudentIDList
once you have it , all you have to do is to replace tokens in previous template
set #sqlTemplate = REPLACE(#sqlTemplate, '##sqlColumnList##', #sqlColumnList)
set #sqlTemplate = REPLACE(#sqlTemplate, '##sqlStudentIDList##', #sqlStudentIDList)
select #sqlTemplate
exec sp_executesql #sqlTemplate
and thats it
if you want to read more about pivot go for msdn
if you want to read about dynamic go for this link
edit: to adjust the query for the question from comment you would have to change #sqlColumnList like that
select #sqlColumnList += ',min(' + QUOTENAME(studentID) + ') as Student' + CAST(studentID as nvarchar(10)) + '_REG,
'''+ studentName + ''' as Student' + cast(studentID as nvarchar(10)) + '_NAME,
'+ cast(studentID as nvarchar(10)) + ' as Student' + cast(studentID as nvarchar(10)) + '_ID'
from #student

Answer 2

This is a pivot of the data. I would perform this slightly different than the other answer. If you know all of the values, then you can hard-code the values.
A static version will be:
select examname,
examendate,
IsNull([Smith, John (14323)], 'false') [Smith, John (14323)],
IsNull([Craft, Peter (14334)], 'false') [Craft, Peter (14334)],
IsNull([Davis, Alan (13432)], 'false') [Davis, Alan (13432)],
IsNull([Newman, Ted (133123)], 'false') [Newman, Ted (133123)]
from
(
select e.examname,
e.examenDate,
s.studentName + ' ('+cast(s.studentnumber as varchar(50))+')' studentNameNum,
'true ' as Flag
from exam e
left join exam_registration er
on e.examid = er.examid
right join student s
on er.studentid = s.studentid
) src
pivot
(
max(flag)
for studentNameNum in ([Smith, John (14323)], [Craft, Peter (14334)],
[Davis, Alan (13432)], [Newman, Ted (133123)])
) piv
See SQL Fiddle with Demo
If your values are unknown then the query will be:
DECLARE #cols AS NVARCHAR(MAX),
#colsNull AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT distinct ',' + QUOTENAME(s.studentName + ' ('+cast(s.studentnumber as varchar(50))+')')
from student s
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
select #colsNull = STUFF((SELECT distinct ',IsNull(' + QUOTENAME(s.studentName + ' ('+cast(s.studentnumber as varchar(50))+')')+', ''false'')'+' as '+QUOTENAME(s.studentName+' ('+cast(s.studentnumber as varchar(50))+')')
from student s
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT examname,
examenDate,' + #colsNull + ' from
(
select e.examname,
e.examenDate,
s.studentName + '' (''+cast(s.studentnumber as varchar(50))+'')'' studentNameNum,
''true '' as Flag
from exam e
left join exam_registration er
on e.examid = er.examid
right join student s
on er.studentid = s.studentid
) x
pivot
(
max(flag)
for studentNameNum in (' + #cols + ')
) p '
execute(#query)
See SQL Fiddle with Demo
The result will be:
| EXAMNAME | EXAMENDATE | CRAFT, PETER (14334) | DAVIS, ALAN (13432) | NEWMAN, TED (133123) | SMITH, JOHN (14323) |
----------------------------------------------------------------------------------------------------------------------------
| Exam 1 | 2013-01-01 12:00:00 | false | false | true | false |
| Exam 2 | 2013-01-01 14:00:00 | true | false | false | true |
| Exam 3 | 2013-01-02 12:00:00 | true | true | false | false |
| Exam 4 | 2013-01-02 14:00:00 | false | false | true | false |
| Exam 5 | 2013-01-03 12:00:00 | false | false | false | true |