Where子句中的问题 [英] Problem in Where Clause

问题描述

Hello Everybody，



以下问题中的问题：

Hello Everybody,

Problem in below query:

DECLARE @First_CName  VARCHAR(50)

SET @First_CName='Source_Id'

SELECT * FROM SourceDest_Details WHERE @First_CName =CAST(45 AS VARCHAR(50))--- This query is not working

但是，

But,

SELECT * FROM SourceDest_Details WHERE Source_Id=45-- This Query is Working

我可以知道原因以及第一次查询是否有可能工作

May i know the reason and if there is any possibility for first query to work

推荐答案

试试这个

try this

DECLARE @First_CName  VARCHAR(50)
SET @First_CName='Source_Id'
DECLARE @SQL varchar(1000)
SET @SQL = 'SELECT * FROM SourceDest_Details WHERE ('+@First_CName+'=CAST(''45'' AS VARCHAR(50)))'
EXEC(@SQL)

您不能像使用变量内容那样动态更改SQL语句的结构。



如果您需要声明是动态的，请查看 sp_executesql [ ^ ]

You cannot dynamically change the structure of an SQL statement like that using variable contents.

If you need the statement to be dynamic, have a look at sp_executesql[^]

如果你应该在where子句中使用像@First_CName这样的动态变量你一定要使用动态T_SQL



DECLARE @First_CName VARCHAR（50），

@lssql nvarchar（100）=''

SET @First_CName ='Source_Id'

set @ lssql ='SELECT * FROM SourceDest_Details WHERE（'+ @ First_CName +'= CAST（''45''AS VARCHAR（50）））'

print @lssql

执行sp_executesql @lssql

if you are supposed to use dynamic variables like @First_CName in where clause you have to surely use dynamic T_SQL

DECLARE @First_CName VARCHAR(50),
@lssql nvarchar(100)=''
SET @First_CName='Source_Id'
set @lssql='SELECT * FROM SourceDest_Details WHERE ('+@First_CName+'=CAST(''45'' AS VARCHAR(50)))'
print @lssql
execute sp_executesql @lssql

这篇关于Where子句中的问题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！