如何使用SQL从文字中获取变量值？

Question

第1部分

DECLARE @A INT
DECLARE @B NVARCHAR(20)

SET @A=123
SET @B='@A'

第2部分

DECLARE @SQL NVARCHAR(MAX)
SET @SQL='SELECT ' + @B

EXEC SP_EXECUTESQL @SQL
--Should return 123

在非动态SQL中直接引用@A对于此任务是不可接受的。

第2部分中的上述内容通常是我想要做的。我了解该变量超出范围，因此无法像上面那样工作。我如何使用@B来获取@A的值？

更新20190322：我实际上忘记了这个问题，并在C＃端而不是在数据库上实现了日志记录，但是如果可能的话，我再次感到好奇。同样，这需要通用，因为我希望将其放在任何存储过程的顶部，并且我不想针对每个sproc对其进行自定义。我在获取参数值的游标中遇到麻烦。这是一个工作示例：

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO    

ALTER PROCEDURE [dbo].[LoggingTest]
    @DateBegin datetime,
    @DateEnd datetime,
    @Person varchar(8000),
    @Unit varchar(8000)
AS
BEGIN
    --BEGIN LOGGING CODE
    DECLARE @String NVARCHAR(MAX)=''
    DECLARE @Parameter_name nvarchar(2000), @type nvarchar(50), @length SMALLINT, @Prec SMALLINT, @Scale SMALLINT, @Param_order SMALLINT, @Collation nvarchar(2000);  
    DECLARE param_cursor CURSOR FOR   
        SELECT
           'Parameter_name' = name,  
           'Type'   = type_name(user_type_id),  
           'Length'   = max_length,  
           'Prec'   = case when type_name(system_type_id) = 'uniqueidentifier' 
                      then precision  
                      else OdbcPrec(system_type_id, max_length, precision) end,  
           'Scale'   = OdbcScale(system_type_id, scale),  
           'Param_order'  = parameter_id,  
           'Collation'   = convert(sysname, 
                           case when system_type_id in (35, 99, 167, 175, 231, 239)  
                           then ServerProperty('collation') end)  
        from sys.parameters
        where object_id = object_id(OBJECT_NAME(@@PROCID))

    OPEN param_cursor  

    FETCH NEXT FROM param_cursor   
    INTO @Parameter_name,@type,@length,@Prec,@Scale,@Param_order,@Collation

    WHILE @@FETCH_STATUS = 0  
    BEGIN  
        SET @String=@String + @Parameter_name + '==' --+ SELECT @Parameter_name --This is part I can't think of a way to do; need to record/capture the value

        SET @String=@String + CHAR(13) + CHAR(10)
        FETCH NEXT FROM param_cursor   
        INTO @Parameter_name, @type,@length,@Prec,@Scale,@Param_order,@Collation
    END   
    CLOSE param_cursor;  
    DEALLOCATE param_cursor;

    --INSERT DATA INTO LOG TABLE HERE
    SELECT OBJECT_SCHEMA_NAME(@@PROCID) + '.' + OBJECT_NAME(@@PROCID) AS [ProcedureName],@String AS [Data],GETDATE() AS [LogTime]
    --END LOGGING CODE    

    /* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
        DO BUSINESS STUFF HERE!
        !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! */
    /*
    BLAH
    BLAH
    BLAH

        DECLARE @Now DATETIME=GETDATE()
        EXEC [dbo].[LoggingTest] @Now,@Now,'Person Value','Unit Value'
    */
END
GO

Answer 1

我不明白您要问的全部内容，但是您可以在上定义变量sp_executesql：

EXEC SP_EXECUTESQL @SQL, N'@A INT', @A = @A