SQL Server - 使用UNPIVOT包含NULL

Question

UNPIVOT不会返回NULL,但我在比较查询中需要它们.我试图避免使用ISNULL以下示例(因为在真正的sql中有超过100个字段:

Select ID, theValue, column_name
From 
(select ID,
  ISNULL(CAST([TheColumnToCompare]  AS VarChar(1000)), '') as TheColumnToCompare
  from MyView
  where The_Date = '04/30/2009'
) MA
UNPIVOT
   (theValue FOR column_name IN 
   ([TheColumnToCompare])
) AS unpvt

任何替代品？

Answer 1

要保留NULL,请使用CROSS JOIN ... CASE:

select a.ID, b.column_name
, column_value = 
    case b.column_name
      when 'col1' then a.col1
      when 'col2' then a.col2
      when 'col3' then a.col3
      when 'col4' then a.col4
    end
from (
  select ID, col1, col2, col3, col4 
  from table1
  ) a
cross join (
  select 'col1' union all
  select 'col2' union all
  select 'col3' union all
  select 'col4'
  ) b (column_name)

代替:

select ID, column_name, column_value
From (
  select ID, col1, col2, col3, col4
  from from table1
  ) a
unpivot (
  column_value FOR column_name IN (
    col1, col2, col3, col4)
  ) b

具有列模式的文本编辑器使这些查询更容易编写.UltraEdit拥有它,Emacs也是如此.在Emacs中,它被称为矩形编辑.

您可能需要为100列编写脚本.

Answer 2

这是一个真正的痛苦.你必须在之前将它们切换出来UNPIVOT,因为没有为行进行生成ISNULL()- 代码生成是你的朋友.

我也遇到了问题PIVOT.丢失的行变成了NULL,ISNULL()如果缺少的值与0.0例如相同,则必须在行中一直包裹.

Answer 3

我遇到了同样的问题。使用CROSS APPLY（SQL Server 2005及更高版本）代替Unpivot解决了该问题。我根据本文找到了一种解决方案，它是UNPIVOT的替代方法（更好吗？） ，我举了以下示例来说明CROSS APPLY不会忽略NULL Unpivot。

create table #Orders (OrderDate datetime, product nvarchar(100), ItemsCount float, GrossAmount float, employee nvarchar(100))

 insert into #Orders
 select getutcdate(),'Windows',10,10.32,'Me'
 union 
 select getutcdate(),'Office',31,21.23,'you'
 union 
 select getutcdate(),'Office',31,55.45,'me'
 union  
 select getutcdate(),'Windows',10,null,'You'

SELECT OrderDate, product,employee,Measure,MeasureType
 from #Orders orders
 CROSS APPLY (
    VALUES ('ItemsCount',ItemsCount),('GrossAmount',GrossAmount)
    ) 
    x(MeasureType, Measure) 


SELECT OrderDate, product,employee,Measure,MeasureType
from #Orders orders
UNPIVOT
   (Measure FOR MeasureType IN 
      (ItemsCount,GrossAmount)
)AS unpvt;


 drop table #Orders

Answer 4

使用动态 SQL 和 COALESCE，我解决了这样的问题：

DECLARE @SQL NVARCHAR(MAX)
DECLARE @cols NVARCHAR(MAX)
DECLARE @dataCols NVARCHAR(MAX)

SELECT 
    @dataCols = COALESCE(@dataCols + ', ' + 'ISNULL(' + Name + ',0) ' + Name , 'ISNULL(' + Name + ',0) ' + Name )
FROM Metric WITH (NOLOCK)
ORDER BY ID

SELECT 
    @cols = COALESCE(@cols + ', ' + Name , Name )
FROM Metric WITH (NOLOCK)
ORDER BY ID

SET @SQL = 'SELECT ArchiveID, MetricDate, BoxID, GroupID, ID MetricID, MetricName, Value
            FROM 
               (SELECT ArchiveID, [Date] MetricDate, BoxID, GroupID,  ' + @dataCols + '
                FROM MetricData WITH (NOLOCK)
                INNER JOIN Archive WITH (NOLOCK)
                    ON ArchiveID = ID
                WHERE BoxID = ' + CONVERT(VARCHAR(40), @BoxID) + '
                AND GroupID = ' + CONVERT(VARCHAR(40), @GroupID) + ') p
            UNPIVOT
               (Value FOR MetricName IN 
                  (' + @cols + ')
            )AS unpvt
            INNER JOIN Metric WITH (NOLOCK)
                ON MetricName  = Name
            ORDER BY MetricID, MetricDate'

EXECUTE( @SQL )