SQL 查询 & unpivot 语法

Question

我有一个权限系统，它定义了用户对某些项目的访问权限。

我需要一个报告页面来显示成员及其对项目的访问权限。

表格需要是这样的：

+---------+--------+--------+------+--------+
| Members | Item 1 | Item 2 | .... | Item N |
+---------+--------+--------+------+--------+
| Member1 |   x    |    +   | .... |   +    |
+---------+--------+--------+------+--------+
| Member2 |   +    |    x   | .... |   +    |
+---------+--------+--------+------+--------+

我有一个 3 表连接查询，用于列出成员和他们可以访问的项目，但我无法将其转换为数据透视语法。

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

这是我的无效查询：

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

以及我收到的错误：

UNPIVOT 运算符中指定的列名“name”与 UNPIVOT 参数中的现有列名冲突。

我创建了一个例子来玩Sqlfiddle

Answer 1

您不需要为此查询使用 UNPIVOT。 UNPIVOT 用于将多列转换为多行。您只需应用 PIVOT 功能即可将您的项目变成列。

我首先建议使用像 row_number() 这样的窗口函数来创建新的列标题，然后应用 PIVOT 函数：

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;

见SQL Fiddle with Demo。然后，如果您有未知数量的值，您的查询将需要使用动态 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;

见SQL Fiddle with Demo