SQL Query & unpivot Syntax - sql

Question

I have a permission system that defines users access to certain items.
I need a report page to show members and their access to the items.
The table needs to be like this:
+---------+--------+--------+------+--------+
| Members | Item 1 | Item 2 | .... | Item N |
+---------+--------+--------+------+--------+
| Member1 | x | + | .... | + |
+---------+--------+--------+------+--------+
| Member2 | + | x | .... | + |
+---------+--------+--------+------+--------+
I have a 3 table joined query for listing the members and the items they can access but I could not convert it into pivot syntax.
Select members.id memberID, members.name memberName, items.name as item
From members
Left Join member_permission On memberID = members.id
Left Join items On items.id = member_permission.itemID
This is the not working query I have:
Select memberName, itemName
From (
select members.id, members.name, item.name as itemName
from members
Left Join member_permission On memberID = members.id
Left Join item On item.id = member_permission.itemID
) p
Unpivot
(itemName For name IN (item.name)) as unp
and the error I receive:
The column name "name" specified in the UNPIVOT operator conflicts with the existing column name in the UNPIVOT argument.
I created an example to play with Sqlfiddle

Answer 1

You don't need to use UNPIVOT for this query. UNPIVOT is used to convert multiple columns into multiple rows. You only need to apply the PIVOT function to turn your items into columns.
I would first suggest using a windowing function like row_number() to create your new column headers, then apply the PIVOT function:
select id, name, Item1, Item2, Item3
from
(
select members.id, members.name, items.name as item,
'item'+
cast(row_number() over(partition by members.id
order by members.id) as varchar(10)) col
from members
Left Join member_permission
On memberID = members.id
Left Join items
On items.id = member_permission.itemID
) d
pivot
(
max(item)
for col in (Item1, Item2, Item3)
) piv;
See SQL Fiddle with Demo. Then if you have an unknown number of values your query would need to use dynamic SQL:
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT ',' + QUOTENAME('item'+cast(seq as varchar(10)))
from
(
select row_number() over(partition by memberid
order by memberid) seq
from member_permission
) d
group by seq
order by seq
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = N'SELECT id, name, ' + #cols + N'
from
(
select members.id, members.name, items.name as item,
''item''+
cast(row_number() over(partition by members.id
order by members.id) as varchar(10)) col
from members
Left Join member_permission
On memberID = members.id
Left Join items
On items.id = member_permission.itemID
) x
pivot
(
max(item)
for col in (' + #cols + N')
) p '
execute sp_executesql #query;
See SQL Fiddle with Demo