这两个查询之间的区别？ [英] difference between these two queries?

问题描述

  SELECT  DBName，ConnString + ' ＃VIJAY＃' + FinanceConnString + ' ＃VIJAY＃' + 
 RptDBConnString  AS  ConStr  FROM  [ DataBase ]  WHERE  Active =  1  

从[database]中选择dbname，connstring作为ConStr，其中active = 1 

给出相同的结果，那么上面两个查询之间的区别是什么？plz解释...



在第一个查询中为什么我们r使用+''＃VIJAY＃''+ FinanceConnString +''＃VIJAY＃''+

RptDBConnString

解决方案

2个查询将给出如果ConnString列为NULL，则结果相同，因为

NULL +任何事都是NULL。

要查看2个查询之间的区别，请使用 ISNULL [ ^ ]

尝试

  SELECT  DBName ，ISNULL（ConnString，' '）+ ' ＃VIJAY＃' + ISNULL（FinanceConnString，'  '）+ ' ＃VIJAY＃' + 
 ISNULL（RptDBConnString，< span class =code-string>' '） AS  ConStr  FROM  [ DataBase ]  WHERE  Active =  1  

SELECT DBName, ConnString + '#VIJAY#' + FinanceConnString + '#VIJAY#' +
RptDBConnString AS ConStr FROM [DataBase] WHERE Active = 1

select dbname, connstring as ConStr from [database] where active=1

giving same result,so what is the diff between above two queries?Plz explain...

in 1st query why we r using+ ''#VIJAY#'' + FinanceConnString + ''#VIJAY#'' +
RptDBConnString

解决方案

The 2 queries will give same result if ConnString column is NULL because
NULL + Anything is NULL.
To see the difference between 2 queries use ISNULL[^]
Try

SELECT DBName, ISNULL(ConnString,'') + '#VIJAY#' + ISNULL(FinanceConnString,'') + '#VIJAY#' +
ISNULL(RptDBConnString,'') AS ConStr FROM [DataBase] WHERE Active = 1

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