如何在SQL Server中查找值 [英] how to find the value in sql server

问题描述

你好，

我有一张桌子这样的学生:-

hello,

I have a table e.g. student like this:-

roll    mark
--------------
1       50
2       60
3       70
--------------

当我进行查询时

when I making query

select mark from student where roll=1

它正在显示

It is showing

mark
-----
50

但是当我写的时候

but when I am writing

select mark from student where roll=4

它正在显示

It is showing

mark
-----

但是我想如果条件不满足，那么它返回零意味着:-

But I want if the condition is not satisfied then it return zero means like:-

mark
----
0

谢谢.

Thanks.

推荐答案

这不是一件好事-这意味着您无法分辨不存在的学生与得分的学生之间的区别零.但是:

That is not a nice thing to do - it means you cannot tell the difference between a student that doesn''t exist, and a student that scores zero. However:

IF EXISTS (SELECT mark FROM student WHERE roll=4)
SELECT mark FROM student WHERE roll=4
ELSE
SELECT 0

但是您应该找到一种更好的方式来组织代码.否则，这将是非常低效的！

But you should find a better way to organise your code instead. If nothing else, this is very inefficient!

select isnull((select mark  from @temptable where id=4),0) as mark

该查询基于SQL 2008数据库.@ temptable是表名.

This query is based on SQL 2008 Data Base.@temptable is table name.

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