sql-server - 没有聚合的 SQL Server 2012 PIVOT

Question

我有以下示例数据：

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

我想显示一个人所属的类别，如下所示：

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

1 和 0 可以用来代替 X 和空白。

对我来说，这听起来像是一个 PIVOT 问题。

Answer 1

有几种方法可以转换数据。有些使用聚合函数，有些则不使用。但即使您正在旋转字符串，您仍然可以应用聚合。

与 CASE 聚合：

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

请参阅带有演示的 SQL Fiddle

静态枢轴：

PIVOT即使值是字符串，您仍然可以使用该函数来转换数据。如果您有已知数量的类别，则可以对查询进行硬编码：

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

请参阅SQL Fiddle with Demo。

动态枢轴：

如果您有未知数量的类别，则可以使用动态 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)

请参阅SQL Fiddle with Demo。

多个连接：

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'

请参阅带有演示的 SQL Fiddle

所有查询都会给出结果：

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