我正在尝试根据三个表中的数据创建一个带有动态列的查询。
这是数据库结构：
学生
studentID int,studentNumber int,studentName nvarchar(100).考试：
examID int,examName varchar(100),examenDate datetime,考试注册：
studentID int,examID int,EXAM_REGISTRATION当学生注册考试时，表格中会添加一条记录。
我想要得到的是一个数据透视表中所有考试和所有学生的列表，以查看哪些学生已经注册了哪些考试，如下所示：
坦率地说，我不知道从哪里开始。
我可以单独查询所有内容并将它们放在一起，但是如何将它们组合成一个查询？
我一直在研究数据透视表，但每个示例似乎只从一个表中查询，并使用数字和函数MIN等AVG。
有人可以帮我吗？
好的，我们走吧
一些数据可以玩
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)
现在是主要部分和解释
首先，您必须获得枢轴查询
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
正如你所拥有的，只需在数据透视声明中更改它的 select 语句和 studentID 列表，你必须动态生成这些部分，所以我们只需复制先前编写的查询并用我们的令牌替换列
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
'
之后，您通过在 tsql 中连接字符串来生成列列表和学生 ID 列表
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
一旦你有了它，你所要做的就是替换以前模板中的标记
set @sqlTemplate = REPLACE(@sqlTemplate, '@@sqlColumnList@@', @sqlColumnList)
set @sqlTemplate = REPLACE(@sqlTemplate, '@@sqlStudentIDList@@', @sqlStudentIDList)
select @sqlTemplate
exec sp_executesql @sqlTemplate
如果你想阅读更多关于 pivot go for msdn 的信息，那就是它，如果你想阅读这个链接的动态 go
编辑：要从评论中调整问题的查询，您必须像这样更改@sqlColumnList
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
这是数据的枢纽。我会执行此操作与其他答案略有不同。如果您知道所有值，则可以对这些值进行硬编码。
静态版本将是：
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
如果您的值未知，则查询将是：
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)
结果将是：
| 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 |