SQL Server 2012 PIVOT without aggregate

Question

I have the following sample data:

Id    Name     Category
-----------------------
1     Joe       A
2     Joe       B
3     Joe       D
4     Mary      A
5     Mary      C
6     Mary      D

I would like to show the categories a person belongs to like so:

Name   CategoryA  CategoryB  CategoryC  CategoryD
--------------------------------------------------
Joe       X          X                     X
Mary      X                     X          X

1's and 0's could be used in place of X's and blanks.

This smells like a PIVOT question to me.

Answer 1

There are several ways that you can transform the data. Some use an aggregate function and others don't. But even though you are pivoting a string you can still apply an aggregate.

Aggregate with CASE:

select name,
  max(case when category = 'A' then 'X' else '' end) CategoryA,
  max(case when category = 'B' then 'X' else '' end) CategoryB,
  max(case when category = 'C' then 'X' else '' end) CategoryC,
  max(case when category = 'D' then 'X' else '' end) CategoryD
from yourtable 
group by name

See SQL Fiddle with Demo

Static Pivot:

You can still use the PIVOT function to transform the data even though the values are strings. If you have a known number of categories, then you can hard-code the query:

select name, 
  coalesce(A, '') CategoryA, 
  coalesce(B, '') CategoryB, 
  coalesce(C, '') CategoryC, 
  coalesce(C, '') CategoryD
from
(
  select name, category, 'X' flag
  from yourtable
) d
pivot
(
  max(flag)
  for category in (A, B, C, D)
) piv

See SQL Fiddle with Demo.

Dynamic Pivot:

If you have an unknown number of categories, then you can use dynamic SQL:

DECLARE @cols AS NVARCHAR(MAX),
    @colsNull AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX)

select @cols = STUFF((SELECT  ',' + QUOTENAME(category) 
                    from yourtable
                    group by category
                    order by category
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

select @colsNull = STUFF((SELECT  ', coalesce(' + QUOTENAME(category)+', '''') as '+QUOTENAME('Category'+category)
                    from yourtable
                    group by category
                    order by category
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')


set @query = 'SELECT name, ' + @colsNull + ' 
              from 
             (
                select name, category, ''X'' flag
                from yourtable
            ) x
            pivot 
            (
                max(flag)
                for category in (' + @cols + ')
            ) p '

execute(@query)

See SQL Fiddle with Demo.

Multiple Joins:

select c1.name,
  case when c1.category is not null then 'X' else '' end as CategoryA,
  case when c2.category is not null then 'X' else '' end as CategoryB,
  case when c3.category is not null then 'X' else '' end as CategoryC,
  case when c4.category is not null then 'X' else '' end as CategoryD
from yourtable c1
left join yourtable c2
  on c1.name = c2.name
  and c2.category = 'B'
left join yourtable c3
  on c1.name = c3.name
  and c3.category = 'C'
left join yourtable c4
  on c1.name = c4.name
  and c4.category = 'D'
where c1.category = 'A'

See SQL Fiddle with Demo

All queries will give the result:

| NAME | CATEGORYA | CATEGORYB | CATEGORYC | CATEGORYD |
--------------------------------------------------------
|  Joe |         X |         X |           |         X |
| Mary |         X |           |         X |         X |