sql-server - 不聚合的旋转

Question

我正在尝试pivot without aggregation ，并且遇到了一点墙壁。

这是我正在尝试使用的示例 T-SQL:

declare @optionalFields table (ParentId int, Name nvarchar(50), Value nvarchar(50));
insert into @optionalFields values (1, 'Field1', 'Foo');
insert into @optionalFields values (1, 'Field2', 'Bar');
insert into @optionalFields values (1, 'Field3', '42');
insert into @optionalFields values (2, 'Field1', 'Bar');
insert into @optionalFields values (2, 'Field2', 'Foo');
insert into @optionalFields values (2, 'Field3', '24');

declare @data table (Id int, Name nvarchar(50));
insert into @data values (1, 'Test record 1');
insert into @data values (2, 'Test record 2');

declare @joined table (Id int, Name nvarchar(50), OptionalFieldName nvarchar(50), OptionalFieldValue nvarchar(50));
insert into @joined
select 
     data.Id
    ,data.Name
    ,opt.Name
    ,opt.Value
from @data data
    inner join @optionalFields opt on data.Id = opt.ParentId

declare @cols as nvarchar(max) = 
    stuff((select distinct ',' + quotename(OptionalFieldName) from @joined for xml path(''), type).value('.', 'nvarchar(max)'), 1, 1, '');

select * into #tmp from @joined
-- just to see that it's returning the expected values (it does)
select
     Id
    ,Name
    ,OptionalFieldName
    ,OptionalFieldValue
    ,row_number() over (partition by Id order by Id) RN 
from #tmp -- this is the FROM clause in the below dynamic-sql query

declare @query as nvarchar(max) = '
    select Id, Name, ' + @cols + '
    from (select Id, Name, OptionalFieldName, OptionalFieldValue, row_number() over (partition by Id order by Id) RN from #tmp) src 
    pivot (max(OptionalFieldName) for RN in (' + @cols + ')) pvt';

execute(@query);
drop table #tmp;

SSMS 给了我 2 个错误:

• Msg 8114, Level 16, State 1, Line 4 Error converting data type nvarchar to bigint.
• Msg 473, Level 16, State 1, Line 4 The incorrect value "Field1" is supplied in the PIVOT operator.

“调试”选择语句返回以下内容:

这篇文章(上面的链接)看起来很有希望，但我似乎无法让它发挥作用。我究竟做错了什么？或者这篇文章完全错误，而我想做的事情是不可能的？

我见过许多类似的SO问题，但它们要么涉及可以“仅适用于”聚合的全数字字段，要么涉及可以作为简单连接实现的已知列 - 我不知道什么我要选择的 OptionalFieldName 值，而 OptionalFieldValue 值是根本无法聚合的字符串，至少据我所知。

Answer 1

我有点困惑为什么你试图使用row_number()来欺骗这个。即使您有字符串值，您仍然可以聚合它 - 您只需使用 max 或 min 即可获得结果。

我总是建议首先尝试使用硬编码值编写查询，尤其是在尝试使用动态 SQL 之前使用 PIVOT 时。我不确定为什么你不能这样编写查询:

select Id, Name, Field1, Field2, Field3
from 
(
  select
     Id
    ,Name
    ,OptionalFieldName
    ,OptionalFieldValue
  from #tmp
) d
pivot
(
  max(OptionalFieldValue)
  for OptionalFieldName in (Field1, Field2, Field3)
) piv;

See a Demo .

如果你真的需要动态SQL，你就这样写:

declare @optionalFields table (ParentId int, Name nvarchar(50), Value nvarchar(50));
insert into @optionalFields values (1, 'Field1', 'Foo');
insert into @optionalFields values (1, 'Field2', 'Bar');
insert into @optionalFields values (1, 'Field3', '42');
insert into @optionalFields values (2, 'Field1', 'Bar');
insert into @optionalFields values (2, 'Field2', 'Foo');
insert into @optionalFields values (2, 'Field3', '24');

declare @data table (Id int, Name nvarchar(50));
insert into @data values (1, 'Test record 1');
insert into @data values (2, 'Test record 2');

declare @joined table (Id int, Name nvarchar(50), OptionalFieldName nvarchar(50), OptionalFieldValue nvarchar(50));
insert into @joined
select 
     data.Id
    ,data.Name
    ,opt.Name
    ,opt.Value
from @data data
    inner join @optionalFields opt on data.Id = opt.ParentId

declare @cols as nvarchar(max);
set @cols = stuff((select distinct ',' + quotename(OptionalFieldName) 
                   from @joined
                   for xml path(''), type).value('.', 'nvarchar(max)'), 1, 1, '');

select * into #tmp from @joined

DECLARE @query  AS NVARCHAR(MAX)

set @query = 'SELECT Id, Name,' + @cols + ' 
            from 
             (
                select Id
                  ,Name
                  ,OptionalFieldName
                  ,OptionalFieldValue
                from #tmp
            ) x
            pivot 
            (
                max(OptionalFieldValue)
                for OptionalFieldName in (' + @cols + ')
            ) p '

execute(@query);

See Demo 。两个版本似乎都给出了您所请求的结果。