将Null值参数传递给动态SQL查询.如何成功执行？

Question

我正在执行动态SQL查询.其中参数是动态传递的.我首先写了类似下面的代码.

DECLARE @Id nvarchar(max);
DECLARE @query nvarchar(max);
SET @Id ='RMH_108'
SET @query ='Select * 
             FROM [A06].[Syn_RMDemand]
             WHERE RMHierarchyId =' + @Id
PRINT @query
EXEC(@query)

然后我写了这个.

DECLARE @Id nvarchar(max);
DECLARE @query nvarchar(max);
SET @Id ='RMH_108'
SET @query ='Select * 
             FROM [A06].[Syn_RMDemand]
             WHERE RMHierarchyId = '''+@Id+''''
PRINT @query
EXEC(@query)

此时间代码已成功执行.由于参数可以为空,我需要将其转换为null.我修改了代码并写了这个

DECLARE @Id nvarchar(max);
DECLARE @query nvarchar(max);
SET @Id = ''
SET @Id = NULLIF(@Id,'')
-- COMMENTED SET @Id ='RMH_108'

SET @query ='Select * FROM [A06].[Syn_RMDemand]
             WHERE RMHierarchyId = '''+@Id+''''
PRINT @query
EXEC(@query)

没有错误.查询崩溃了.
有人提出这类问题吗？

Answer 1

无需将其转换为 NULL，只需检查您的值

DECLARE @Id nvarchar(max);
DECLARE @query nvarchar(max);
 SET @Id = ''


                            -- COMMENTED SET @Id ='RMH_108'
SET @query ='Select * FROM [A06].[Syn_RMDemand]
             WHERE RMHierarchyId = '''+@Id+''''
PRINT @query
EXEC(@query)