Question

I am trying to get a handle on manipulating table data into more visually appealing formats for output. This could be part of the problem as what I want may be intended for separate reporting software.

I have a table that looks like this

teacher    student
----------------------
teacher1   Bob
teacher1   Jim
teacher2   Sam
teacher3   Bill
teacher3   John
teacher3   Eric

I want a table that looks something like this:

teacher1    teacher2    teacher3
---------------------------------
Bob         Sam          Bill
Jim         null         John
null        null         Eric

So I tried stuffing all the teacher names in a variable and then using a Pivot but since I have to choose an aggregate I can only get the Max or Min student like this:

DECLARE @teacherList AS VARCHAR(max)

SELECT @teacherList = Stuff((SELECT DISTINCT',[' + teacher + ']'
                              FROM myTable
                              FOR xml path('')), 1, 1, '')

DECLARE @dynamic_pivot_query AS VARCHAR(max)

SET @dynamic_pivot_query = 'select' + @teacherList + 
'from 
(
    SELECT [teacher],[student]
    FROM [dbo].[myTable]
) as S
Pivot
(
    MIN([student])
    FOR teacher IN (' + @teacherList + ')
) as P
'
EXEC(@dynamic_pivot_query)  

The result of this is:

teacher1    teacher2    teacher3
---------------------------------
Bob         Sam          Bill

Assuming the following:

1. # of teachers and their names are unknown (variable)
2. # of students per teacher is unknown and likely different for every teacher

Is there a way to do this?

Answer 1

You can use row_number to get the result you want.

SET @dynamic_pivot_query = 'select ' + @teacherList + 
'from 
(
    SELECT [teacher],[student], row_number() over(partition by teacher order by student) as rn
    FROM [dbo].[myTable]
) as S
Pivot
(
    MIN([student])
    FOR teacher IN (' + @teacherList + ')
) as P
'

Update:
To remove the SQL Injection vulnerability you should use quotename to properly quote your field list.

SELECT @teacherList = Stuff((SELECT DISTINCT',' + quotename(teacher)
                              FROM myTable
                              FOR xml path('')), 1, 1, '')