sql - 如何在SQL中计算一条记录中具有空值的所有字段？

Question

有没有办法计算除 PrimaryKey 列之外的特定记录的所有具有空值的字段？

Example:

ID  Name    Age    City     Zip

1   Alex    32     Miami    NULL
2   NULL    24     NULL     NULL

作为输出，我需要得到 1 和 3。没有明确指定列名。

Answer 1

declare @T table
(
  ID int,
  Name varchar(10),
  Age int,
  City varchar(10),
  Zip varchar(10)
)  

insert into @T values 
(1, 'Alex', 32, 'Miami', NULL),
(2,  NULL,  24,  NULL,   NULL)

;with xmlnamespaces('http://www.w3.org/2001/XMLSchema-instance' as ns)
select ID,
       (
          select *
          from @T as T2
          where T1.ID = T2.ID
          for xml path('row'), elements xsinil, type 
       ).value('count(/row/*[@ns:nil = "true"])', 'int') as NullCount
from @T as T1

结果:

ID          NullCount
----------- -----------
1           1
2           3

更新:

这是一个更好的版本。感谢 Martin Smith .

;with xmlnamespaces('http://www.w3.org/2001/XMLSchema-instance' as ns)
select ID,
       (
          select T1.*
          for xml path('row'), elements xsinil, type 
       ).value('count(/row/*[@ns:nil = "true"])', 'int') as NullCount
from @T as T1

更新:

并使用更快的 XQuery 表达式。

;with xmlnamespaces('http://www.w3.org/2001/XMLSchema-instance' as ns)
select ID,
       (
          select T1.*
          for xml path('row'), elements xsinil, type 
       ).value('count(//*/@ns:nil)', 'int') as NullCount
from @T as T1